Saxioliken

Yea , if your undervolting is enabled of course... just when you overclock pay attention to the CPU temperatures or else you will burn it ...

Undervolting is when you keep clock speeds at stock but you lower the voltage. Overclocking is when you increase the clock speeds. While overclocking, you might also raise, lower, or even keep the voltage the same as stock.
Undervolting is totally safe as long as you make sure the undervolt is stable. Overclocking can be fine as long as you make sure temps, noise, and voltage are still reasonable.
 
What gpu do you have?

Undervolting is where if a GPU uses 1v to stay at say 1750mhz, then you will force it to run at .975v. this leads to less heat and less wattage drawn. Overclocking is when the max the GPU will go is say 1800mhz, then you again tell it to run say 50mhz higher. This way it goes slightly faster getting marginally better performance.
 
If undervolting is enabled, then yes it is safe. Overclocking tho is different. Yes if the GPU stays below 80 at games, but no if it doesn't.

An external HDD is just a normal one in a fancy enclosure with an adapter. Simply open it up and remove the harddisk and you'll be fine

that i cant answear but you should save all you importan files on that one

i mean just save all the files on a usb or something else and use it as long as you can. just buy a new hdd or ssd in the near future

It doesn't mean the drive is damaged to the point of failure, I've had drives last years sounding like that, just take care to have important documents backed up and you will be fine 

but does it make the sound? if not you know that its the harddrive

That HDD sounds like it's on it's last legs.

could maybe be the harddrive(if thats what you are using) they can get pretty noisy if they get old. might also be why its taking some time to boot up.

I'm not sure, but i think is the Hard Drive. Maybe that's the reason also that takes too long to boot up

Under specs...
 

All he has to do is open dxdiag.exe like the fastest easiest way to find it out.

or follow these steps 
On the keyboard, hold down the WINDOWS key and then hit R. In the Run window, type MSINFO32 and then click OK. In the System Information window, click the File menu and then Save. Set the desired folder to save to, enter a file name, and then click Save. and share the NFO file 

it's an atx board. you have 6 Sata ports to plug in the 2.5 SSD drive but 4 of those are slower 3Gb/s. make sure you plug the SSD in faster 6Gb/s port for best performance. 

1) Get the model of your MB, like the exact model, then look up it's form factor and get a compatible case. Although unless it's from dell it's likely ATX
2) If you're not overclocking it should be fine with the stock cooler.
3) A SATA SSD will work by default.  An NVME SSD won't (you might be able to use it as secondary storage but  older systems can't boot from them)

If the board is ATX, a full size ATX case should work.
 
If you cant overclock it wont help much if at all.  Larger coolers are just quieter.
 
Older boards require SATA SSD's instead of M.2.  The easiest way to figure this out is that SATA SSD's look like laptop hard drives.

He can run this to find exactly which CPU and other stuff he has. https://www.cpuid.com/softwares/cpu-z.html
 
Most likely it's the GPU holding you back though. Pick up a desktop 1050ti for it and it should be faster than your laptop again.

No, the components are just that out of date.  The HD 7850 is, at best with a good OC, somewhere between a GT 1030 and a GTX 1050.

It doesn't hurt to give your computer a good cleaning anyway, but you don't have to guess.  If you see your CPU thermal throttling in afterburner you'll know.

according to future mark(GPU benchmark) your laptop's GPU is 49% faster than you desktop's GPU. 

Also 2011 CPU which would be Sandy Bridge CPUs, but there is no 3.5GHz  Sandy Bridge i5. This probably means your PC has original dual core i5

Look for a tutorial on youtube.
Yes it is called a stick and it might help a little bit (depending on the game and your current system) but you wont really see a huge improvement in games without upgrading your GPU.