DHelios

As Oshino Shinobu stated, you can just install the extra module and see what happens. Either it works, or it doesn't. As long as you don't do anything strange, it should not cause any permanent damage if it doesn't work.
 
That answers wether or not you can install the extra module. That just leaves wether you should.
 
AlexTheRose pointed out that it might make your system run in single-channel mode. Here's what that comes down to:
 
You are currently using two identical sticks of RAM in two matched slots on your mainboard. This allows the memory controller to access the memory in dual-channel mode. Being able to communicate with two modules at once means that the available bandwidth between your CPU and your RAM is a lot wider. If your programs are reliant on higher memory bandwidth, this is a nice speed boost. This technology also generally requires the same memory to be installed in the two channels.
 
Adding a third module means that one memory channel has 4GB, the other has 8GB. Whilst it is possible for some motherboards to respond to this by making the first 8GB nice and dual-channel fast and the last 4GB to be single-channel 'slow', most motherboards will simply switch off dual-channel mode and run in single-channel mode. If you are not reliant on the speed of your memory but rather need that extra 4GB for its sheer capacity, you may actually be better off with 12GB of single-channel RAM.
 
To figure out how your mainboard handles this, the easiest way is to, again, just install the module and see what happens. After that, you can determine which is the better choice for you: 8GB of 'fast' memory, or 12GB of 'slow' memory.

The Ryzen 7s that have been released so far, are very competitive compared to Intel's Broadwell-E line of processors, not so much the Kaby Lake i7s.
 
If gaming is your sole purpose for the machine, the Kaby Lake i7 is the way to go. If it's just for CS:GO, it may be interesting to see what the performance difference for that particular game may be to a Kaby Lake i5.
 
That said, things may become interesting in a few months, when Ryzen 5 and Ryzen 3 come out. If, like Intel, AMD has higher clock speeds on their fewer-core processors, then the Ryzen 5 hexa- and quad-core processors may actually be a better match for Kaby Lake than the currently available Ryzen 7s. At least where gaming is concerned...

The Ryzen 7s that have been released so far, are very competitive compared to Intel's Broadwell-E line of processors, not so much the Kaby Lake i7s.
 
If gaming is your sole purpose for the machine, the Kaby Lake i7 is the way to go. If it's just for CS:GO, it may be interesting to see what the performance difference for that particular game may be to a Kaby Lake i5.
 
That said, things may become interesting in a few months, when Ryzen 5 and Ryzen 3 come out. If, like Intel, AMD has higher clock speeds on their fewer-core processors, then the Ryzen 5 hexa- and quad-core processors may actually be a better match for Kaby Lake than the currently available Ryzen 7s. At least where gaming is concerned...

No, they have no need to, and are already priced competitively for the Ryzen 7 lineup. If you want a cheaper Ryzen CPU, wait for Ryzen 3 and 5. 

The IT Crowd comes to mind...
 
"Uh, the button turns it on?"
"Yeah. You-- You do know how a button works, don't you? No, not on clothes..."
"No, no, there you go. There you go, I just heard it come on."
"No, no, that's the music you hear when it comes on."
"That's the music you hear-- I'm sorry, are you from the past?"

The Ryzen 7s that have been released so far, are very competitive compared to Intel's Broadwell-E line of processors, not so much the Kaby Lake i7s.
 
If gaming is your sole purpose for the machine, the Kaby Lake i7 is the way to go. If it's just for CS:GO, it may be interesting to see what the performance difference for that particular game may be to a Kaby Lake i5.
 
That said, things may become interesting in a few months, when Ryzen 5 and Ryzen 3 come out. If, like Intel, AMD has higher clock speeds on their fewer-core processors, then the Ryzen 5 hexa- and quad-core processors may actually be a better match for Kaby Lake than the currently available Ryzen 7s. At least where gaming is concerned...

That's definitely a scam. They've probably collected a small amount of information about you from some hack or leak, and are using the call to try and social-engineer more out of you.
 
These calls usually lead to the 'Microsoft engineer' asking permission to remote access your computer. From there they'll do some pseudo-technical things before recommending you purchase some software or service that will supposedly fix your supposed problem. Alternatively, they may use your system access to collect additional (financial) data or to encrypt your data and have you pay to get it back.
 
It's sadly a common thing, which means that sadly, people fall for it. I've had to deal professionally with victims of such scams, and it's not pretty.
 
 

It's the bare minimum of what I'd consider recommending to anyone. Take your time when doing anything, as Sierra is very much optimised with SSDs in mind. As soon as you can, you'll want to at least perform that upgrade.
 
That said, if it's in good condition it's still a decent computer for not much money. Ar for things to check:
See if the seller will run an app like Coconut Battery so you can get an idea of what state the battery is in (not much use to a mobile device that isn't mobile for more than five minutes) Check the underside. This model is known for its rubber bottom peeling off. If it's wavy it's likely to come off soon. If it's very clean and has no serial number printed on it (near the little embossed text) the bottom case has already been replaced, and you should be good. If you can get a Mid-2010 or newer MacBook Pro for not too much more it'll be worth the investment on the aluminium unibody alone. It'll also net you a GeForce 320M upgrade from the 9400M...

Just Don't Drop It.

Go here: https://ninite.com/
 
Choose the stuff that you will use. I personally like to install Chrome, Firefox, Skype, Steam, VLC, and Malwarebytes after almost every fresh Windows install.

If it's for gaming --and League and WoW in particular-- and you're on a budget... I'd recommend against an i7, a fancy motherboard, a lot of RAM and a high-end graphics card.
 
The case, go wild. You don't want to have to upgrade that later. Getting a decent mainboard (really, anything ASUS is good quality, don't spend extra on fancy 'gamer' or overclocking features that you're not going to use). Stick a single stick of 8GB RAM in there now so you can easily upgrade to 16GB later. And go easy on the graphics card: League would play well even with the integrated graphics on an i5, and WoW gets quite the boost from even a simple graphics card.
 
If you're looking to buy her an awesome computer, then mimic the system you have now. If you're looking to keep the budget low, get something that suffices now (but with a solid base -- case, PSU, mainboard) and upgrade later.

If it's for gaming --and League and WoW in particular-- and you're on a budget... I'd recommend against an i7, a fancy motherboard, a lot of RAM and a high-end graphics card.
 
The case, go wild. You don't want to have to upgrade that later. Getting a decent mainboard (really, anything ASUS is good quality, don't spend extra on fancy 'gamer' or overclocking features that you're not going to use). Stick a single stick of 8GB RAM in there now so you can easily upgrade to 16GB later. And go easy on the graphics card: League would play well even with the integrated graphics on an i5, and WoW gets quite the boost from even a simple graphics card.
 
If you're looking to buy her an awesome computer, then mimic the system you have now. If you're looking to keep the budget low, get something that suffices now (but with a solid base -- case, PSU, mainboard) and upgrade later.

@Sylentic Here's what I put together. Normally, I wouldn't spend this much on a keyboard on such a tight budget, but it's an awesome keyboard at a very cheap price.
 
Also, this Pentium has hyperthreading. It's part of the new Kabylake lineup and performs on par with a Core i3 6100.
 
Also, I used PCPartPicker Germany, but I imagine import fees won't be too high, as they're your immediate neighbours.
 
PCPartPicker part list / Price breakdown by merchant
CPU: Intel Pentium G4560 3.5GHz Dual-Core Processor  (€81.86 @ Mindfactory) 
Motherboard: ASRock H110M-HDS Micro ATX LGA1151 Motherboard  (€53.99 @ Amazon Deutschland) 
Memory: Crucial 8GB (1 x 8GB) DDR4-2133 Memory  (€48.34 @ Amazon Deutschland) 
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive  (€51.99 @ Amazon Deutschland) 
Video Card: Zotac GeForce GTX 1050 2GB Mini Video Card  (€125.99 @ Amazon Deutschland) 
Case: Zalman ZM-T1 PLUS MicroATX Mini Tower Case  (€26.11 @ Amazon Deutschland) 
Power Supply: XFX ProSeries 450W 80+ Bronze Certified ATX Power Supply  (€51.06 @ Amazon Deutschland) 
Monitor: Hannspree HE225DPB 21.5" 1920x1080 Monitor  (€93.99 @ Amazon Deutschland) 
Keyboard: Ducky Shine 4 Wired Gaming Keyboard  (€43.02 @ Amazon Deutschland) 
Mouse: Cooler Master Xornet II Wired Optical Mouse  (€12.90 @ Amazon Deutschland) 
Other: Windows 10 OEM Key (Kinguin) (€24.00)
Total: €613.25
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-01-10 14:37 CET+0100
 

Still, a very, very special laptop...

That's a very special laptop!
(You're also trying to cram DDR3 modules into a DDR4 slot...)

http://www.samsung.com/us/computing/memory-storage/solid-state-drives/ssd-850-evo-m-2-500gb-mz-n5e500bw/
 
This is the M.2 version of the Samsung 850 EVO.
 
The 850 EVO comes in 2.5", mSATA and M.2 form factors. All of them use the SATA connection protocol, so their performance is identical or near-identical. The M.2 version would however not work on your mainboard, as your M.2 slot only supports PCIe-based SSDs!

Samsung support already gave you the correct answer. 512 GB is the same as 477 GiB. SSDs and HDDs are sold in GB (or TB), but Windows and many programs use the slightly different binary units GiB (and TiB).

Actually, the Define R5 has pretty impressive stock fans. Then again, BeQuiet! is one of my go-to-brands for aftermarket fans... I'd think you'd make a good purchase with either case without having to go out and buy new fans right away.
 
I love the look of Fractal's Define line. I've got two R3s, and I've built many systems for customers in XL R2s, R4s, R5s, S's and Mini's. They're a joy to work in!

Actually, the Define R5 has pretty impressive stock fans. Then again, BeQuiet! is one of my go-to-brands for aftermarket fans... I'd think you'd make a good purchase with either case without having to go out and buy new fans right away.
 
I love the look of Fractal's Define line. I've got two R3s, and I've built many systems for customers in XL R2s, R4s, R5s, S's and Mini's. They're a joy to work in!

SPCR Had originally built a silent gaming rig in the R4 for a review, and got the R5 sample in partway through testing. After testing they swapped the system to the R5 to compare the R4 and R5 with the same hardware in the same tests. The R5 stock fans were on par with the aftermarket ones they'd used in the R4.
source: http://www.silentpcreview.com/article1422-page1.html

https://www.amazon.com/MITSUMI-D509V3-1-2MB-FLOPPY-DRIVE/dp/B00B875KJU/ref=sr_1_1?ie=UTF8&qid=1480936961&sr=8-1&keywords=5.25+floppy+drive
 
Crazy enough?

https://www.amazon.com/MITSUMI-D509V3-1-2MB-FLOPPY-DRIVE/dp/B00B875KJU/ref=sr_1_1?ie=UTF8&qid=1480936961&sr=8-1&keywords=5.25+floppy+drive
 
Crazy enough?

Getting a good PSU is definitely worth it, as you'll be wiring it into most components in your computer. Of everything you put in there, the PSU is most likely to take other components with it if it fails.
 
That doesn't mean that the PSU has to be 80+ Bronze, Gold or Anything-certified. Those certifications only show a certain level of power efficiency. It's good for the environment and it's good for your power bill, but it comes at a higher initial cost. It doesn't guarantee a level of quality, other than that efficient PSUs tend to have better quality components to reach their more efficient performance.
 
That said, a power-efficient PSU turns more electricity into electricity, and turns less electricity into heat. Lower heat output reduces the need for cooling, so fan speeds may be lower in these parts. Like with the component quality, this is often the case, but is not a guarantee.
 
In the end, you'll be looking for a PSU that is reliable and well-built. I believe there's a post somewhere on this forum that lists what PSUs definitely not to buy and which ones are considered safe investments. (I believe the SuperNova GS's come out as acceptable quality in that list.) Have a look for that!
 
edit:
@Matt_98 just provided a link to just that list. Thanks Matt!