Constant computer freezing

[cccarrow]

System specs:
AMD FX9590
MSI 990FXA Gaming ATX
GTX 980
Corsair Vengeance Pro Red 16 GB

Custom built computer built by a friend of mine, worked with no issues for a year and a half. 6 months ago, the problem started. After gaming for an hour or two, the computer would freeze in the middle of whatever I'm doing, no matter what I'm doing, no matter what programs are running. After the first crash, the subsequent crashes exponentially increase in frequency until it almost crashes on startup.
It can't be overheating, my temperature monitor says all my hardware is under 40° at all times, the CPU and GPU are independently water cooled. All drives are without errors, all drivers are fully updated, all unnecessary software has been removed, and multiple antivirus scans have been run with different programs revealing nothing, and the problem occurs offline. I have brand new RAM, even though the problem occured with the old RAM too, no system logs are created to give a hint on the cause, I swapped out the GPU to a GTX 550TI as a test and it still crashed. Please help, I'm at my wit's end here

 

[marksavio]

have you tried running a check disk on your hard drives? failing drives is a common cause of freezes. if all else fails, i would usually do a clean isntall of windows and reinstall all drivers and making sure the BIOS is the latest. this is always my last resort and more than half the times the problem just goes away.

 

[cccarrow]

I've already checked all my drives, and they're perfect. I was hoping to avoid a complete reinstall if possible because I need the computer for work, but it appears I'm all out of options