sjain

I mainly went for B560 because it unlocks RAM speeds and is cheaper, but the support for 11th gen is also nice C:

No meaningful difference for your build, but in the interest of being thorough, it might be ever so slightly less efficient at the load of this PC by like a tenth of a percent. The 650W version is the better buy for sure.

Yeah, it'll be fine.
The 10400 is a good choice for value. The 11400 would be even better as @Downkeyhas selected in their build.
The one you chose will do fine for this.
It's a good board, but the B560 board that @Downkeyselected is cheaper and better in some ways.
 
The 2x8GB kit that @Downkeyselected is cheaper and will perform better vs the 1x16GB kit that you had found. Crucial, owned by Micron, is good RAM.
Looks good. 👍
650W is obviously overkill, you could get by with 300W, but it's a really good unit for a good price. Nice find.

this would be much better imo 
PCPartPicker Part List
CPU: Intel Core i5-11400 2.6 GHz 6-Core Processor  (£169.99 @ Amazon UK) 
CPU Cooler: be quiet! Pure Rock Slim 2 CPU Cooler  (£25.27 @ Overclockers.co.uk) 
Motherboard: ASRock B560M-ITX/ac Mini ITX LGA1200 Motherboard  (£95.99 @ Amazon UK) 
Memory: Crucial Ballistix 16 GB (2 x 8 GB) DDR4-3200 CL16 Memory  (£75.59 @ Amazon UK) 
Case: Fractal Design Core 500 Mini ITX Desktop Case  (£54.16 @ CCL Computers) 
Power Supply: Corsair TXM Gold 650 W 80+ Gold Certified Semi-modular ATX Power Supply  (£53.05 @ Amazon UK) 
Optical Drive: Lite-On iHAS124-14 DVD/CD Writer  (£15.89 @ CCL Computers) 
Speakers: Logitech Z200 0 nW 2.0 Channel Speakers  (£26.66 @ Amazon UK) 
Webcam: Logitech C270 Webcam  (£24.99) 
Total: £541.59
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2021-05-25 13:21 BST+0100

As for the thermal paste, it might not be the best performance, but I think it will do for the build

Damn thats an old system. Brings back memories back when this shit is new (mostly ass, but eh)
Most UPS i know usually also comes with power filter and surge protector as well, but most consumer stuff i know doesnt have user hot swappable batteries. You gonna have to tear it down and know how to replace cells.
You need to look at your Volt Amps (VA), its basically your capacity in UPS industry. I ran your system to the calculator and you gonna need around 1200 to 1300VA to even have few minutes to alt+f4 (or save) everything. Good news is you can get larger than that for above 200 pounds, but im saying that 1500 or above is more safe.

So you followed the first part of my advice and did install with only one of the drives attached...
 
Like I said I know Windows really doesn't get along well with other partitions on the install drive but completely separate drives are another story and you wont have to worry if you only have one drive attached during install. Its not like windows can complain about a drive that isn't even attached.

yeah , hence why the manual says where the primary gpu goes. 

I go with uncooked rice for CPUs.  Cooked rice for GPUs.  Worked out well for me so far.
 
thats for size, i dont actually use rice.  because someone will give me shit about using Rice to cool my CPU/GPU....you know who you are.

Oh man, you wrote that a few seconds before me! :angryreactionsonly:

Unless the Thermal Paste you're using is electrically conductive, there's no such a thing as too much thermal paste.
Linus (well, technically Luke, but you got the point) did a video about this, Jay did a video about this, Steve from GN did a video about this, and I'm pretty sure 90% of the major YT channel made videos about it.

Looks fine to me. Since MX-4 is non-conductive (really ill-advised to use conductive paste on GPUs), it's better to put a bit too much than a bit too little.

Within reasonable bounds, there is no such thing as too much paste. Mounting pressure SHOULD push the excess paste away. It may be messy, but as long as it's not an electrically conductive or corrosive paste, it shouldn't matter.

No, manu's go gloopy on  GPUs; not sure why but that's normal! Factory Job.


You could have used less, a small pea size would squish perfectly. You can too remove it to see the spread and re-apply it, there's no rules there.

We typically avoid metal contact with conducting paste with silver/etc.

it looks like your cable contracted boneitis

idk

to protect yourself from future damage from black outs / brown-outs, you may want to invest in a UPS (uninterruptible power supply), which is basically a big battery that can keep your PC running for long enough to shut it down smoothly. These can be quite expensive mind you. 
You will want to find one that will support the power requirement of your PC. You can use this tool:
https://outervision.com/power-supply-calculator
 
Also your PC should be fine, you can use windows built in System File checker tool to check for consistancy: 
 
details here:
https://support.microsoft.com/en-au/help/929833/use-the-system-file-checker-tool-to-repair-missing-or-corrupted-system
 

@sjain If you have a surge protector then everything is fine.
Power-cuts mostly lead to data loss but they don't damage your system.