PC Restarts Whilst Gaming

[VerosHD]

In the past few months, my PC has been gradually getting worse. Sometimes, and I mean only sometimes because almost a quarter of the time, my PC is just fine, my PC randomly decides to restart (no BSOD or anything, just shuts off then reboots itself) when I'm about 20 minutes to an hour into playing a game. This happens on mostly every game except for the old source engine games (which I think I just haven't played them enough for it to actually shut down). I have absolutely no idea what's causing this because I've looked into pretty much everything.

Things I've done:
- Replacing PSU with Corsair RM1000w
- Disabling automatic restart on critical error in Windows
- Installing different versions of my GPU drivers (multiple times)
- Memtest86+ test (Ran for 3+ hours with no errors)
- Bios update (Stopped problem for one night but restarts started happening again today)
- Prime95 test (CPU passed flawlessly, stayed at around 50c the whole time)
- Monitoring temps (None of my temps go above 60c-70c)
- Clearing CMOS
- Taking out two HDDs

My specs:
- Gigabyte Geforce GTX 770 2GB
- 3 x 1TB HDDs (Seagate, WD Blue, WD Green)
- 16GB (4x4) Dell 1600MHz RAM
- Corsair RM750 PSU (returned 1000w because it didn't fix problems)
- i7 3770 (not overclocked)
- Corsair H60 liquid cooling
- MSI Z77 a g45 gaming motherboard

I've established so far that it's not my BIOS, PSU or temps.

If I'm forgetting anything, just tell me.

 

[Tmagic650]

Which hard drive is the boot drive? WD blue and green drives are not good...

 

[VerosHD]

Which hard drive is the boot drive? WD blue and green drives are not good...

I use my WD Blue drive as my main.

 

[Tmagic650]

Try running a test on this hard drive...

 

[Spykezxp]

Have you Overclocked the GPU? You say that it happens on Games, but did not mention if you overclocked your graphics card or not. If you have, try lowering the settings a bit and see if you can game longer.
How long did you run the Prime95 test for?