Now, to the problem. I was getting random lock ups. These lock ups would become more frequent until the point where I am now; the computer won't boot, save for safe mode. I acutally had a lock up in safe mode when I was having a lot of chrome tabs up, foobar2000 playing and windows live messenger logged on and a movie playing in MPC.
I believe this could be related to the fact that I installed 2 SATA hard drives. I can't recall it occuring before, and it didn't start at once when I installed my new hard drives. But again, I can't remember it before, and that's the only hardware change I've done.
At that point I had the system, 3 SATA-drives, 1 IDE-drive (all 7.2k rpm), 2 92mm fans, 3 120mm fans.
I reinstalled Windows as to have a clean version to check for software problems. Windows booted the first time, I proceeded to install VGA drivers and reboot. It wouldn't load past the "welcome"-screen, once more. To be fair, Windows also automatically installed some drivers. Onboard sound and PCI sound card. Alas, I don't believe that to be relevant.
After this issue I unplugged the IDE-drive, 2 sata-drives and both 92mm fans, since I can boot and have the computer running, but it still, frustratingly, locks up.
I've ran memtest86+ for 7 hours, no errors. I moved my graphics card to another computer (520W no brand PSU) where I've ran FurMark, it worked. I didn't really stress the card since that doesn't seem relevant at all to my errors.
Also, rather obvious, but if you have any Overclocking, remove it. You just select fail safe settings in BIOS.
Check SMART data on your HD's to see if there's any issue there. Can be viewed in BIOS.
IF PSU swap doesn't work, swap components for known good ones, or place current components in a working PC until you find the one that's not working.
The CPU overclock is stable, I've run 4 hour tests in PRIME without errors. Maybe I should let it stay on overnight to see if it's stable. But a CPU fail shouldn't end up with the graphics freezing with sound still playing, should it? Besides, it's been stable for about a month. Using a Audigy 2 PCI sound card if it matters in any way, I couldn't think of any so I didn't mention it earlier.