I've been without a PC for about 5 months now, after having a motherboard, processor and power supply all come back faulty. So now I've got effectively a brand new machine, with a Gigabyte P35-DQ6, Q9550, and a RAM upgrade to 4gb of Corsair PC2-8500 CL5. I put everything together with my Thermalright Ultra-120 Extreme in there as well, and started setting everything up.
Then I found that if I ran Prime95 my entire PC just freezes, and the same story if I try to do a memtest in Windows - I get 0.2% coverage then the whole thing freezes, no response. I went to the bios and underclocked the processor to a 6x multiplier (2.0Ghz) and used a 2.0 FSBRAM ratio which put the RAM at 666MHz, but no change, so I put the RAM chips up to their specified 2.1V. Then I tried taking out the chips and just running one at a time, but memtest in Windows failed on both chips after around 15-25% coverage, although Prime95 didn't freeze my PC. I then dropped the RAM voltage back down to 1.8V and loosened the timings to 5-7-7-24, and started running memtest86 off a UBCD - I managed to complete 1 pass on a chip and (after falling asleep) 4 passes on the other with no problems, but with both chips in memtest86 just stopped after about 7 minutes, completely frozen.
I also checked the temperatures with HWMonitor and the CPU cores were showing at around 39-45 celsius, GPU at about 55-60, so nothing that unusual, and they didn't have time to heat up before it crashed so I doubt it's temperature related. It's just really killing me after waiting 5 months to get my system back... I've got no idea what to do if I can't get memtest to actually complete.
Any ideas would be appreciated.