Did you test the heat idea?
That is, the old leave the cover off and point a fan at it test?
My comp shuts off randomly whenever I run anything that is graphics heavy. Examples...just about any gaming, videos, etc. I know it's not heat related because it will shut down even seconds after loading up a game or video. On the other hand, it will let me play for hours other times and not shut off. I have 7 case fans, both graphics cards are Nvidia GTX 570's with fans running in SLI and the motherboard has liquid cooling. 8 gigs of RAM, 2 500 gig hard drives running in RAID 0. Windows 7 64 bit.
This computer is a beast but this has been happening since I got it about 2 years ago. I sent it back to the manufacturer 3 times and they have replaced almost everything but it is still doing it. The warranty is now up on it so I'm on my own. I've asked everyone I know but no one seems to be able to figure it out.
It's not BSOD or normal shut down. It is just instantly off. No warnings or anything. It always starts right back up with no problems. The only thing I can think of is that the system is set to shut off at a lower temp than it should be. I've run Speed Fan and the temps are never high.
Any help with this would be greatly appreciated. I'm to the point that I just want to sell it and start over. Please let me know if any other info is needed. Thanks!