New System Unstable Even Below Stock

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 FSB:DRAM 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.

Buy a large baseball bat, visit the person / company who sold / returned the machine to you, and hit them with it.

No, it won't fix your computer, but it might just make you feel better!

A quick google shows a very limited QVL support list for your motherboard @ DDR2 1066: there's a noticable lack of 2GB modules. You could try flashing to the latest stable BIOS - version F4 includes some specific memory enhancements, but it's rarely a bad idea to get the latest version (F7, in this case).

Anyway, if you browse the Gigabyte product page you should be able to find some help...

The mobo looks at fault, maybe it's just not compatible with the RAM. If you could try another set you could check whether that was the case.

Mind you I see that you have a Hiper Type-R 580. Could be on its way out.

No, the Hiper Type-R has already been out. It destroyed my old motherboard and processor. :)

As for the company who've been messing me around for the last 5 months, that would be Scan. Although they did flash the BIOS to the latest version, so can't fault them on that ;)