Just built my new system, and from the off I have been suffering from random memory errors which I cannot pin down.

I had bought a G6950 CPU, a Gigabyte H55M-S2 motherboard and two sticks of Geil 2GB 1333MHz DDR3, with an existing Radeon HD4650, DVDRW drive and a new Samsung 500GB SATA HDD (to replace the one I managed to brick when I was putting everything together! GRR!).

The initial install of Win7 64 bit seemed to go ok initially until I started Windows for the first time and it just rebooted without warning when I started to load my programs. First, I remembered the case I had put it in used to have a shorting issue with my old motherboard, so changed it. Still random reboots and then failed launch into Windows, sometime accompanied with windows messages of "instruction...referenced memory. The memory could not be read" and sometimes BSOD with messages about "page file memory" etc. Similar messages even showed up when I tried to reinstall windows on some attempt from the initial setup. Upgraded BIOS to latest (F4), no change, default or optimized settings in BIOS made no difference.

I ended up changing the RAM sticks because I'd mistakingly bought Single Channel RAM and I thought this was the cause, and put in some OCZ sticks which I checked were compatible on the Gigabyte website. Initially things seemed OK, but then the failed Windows launches returned. Whipped out the graphics card to just use the onboard RAM, and again seemed to work OK initially, but turning back on the next day, memory errors again when I get into Windows ("instruction...referenced memory. The memory could not be read") or just failed boot attempts. I've tried with just one stick of RAM in now, and still the same.

My main culprit is the processor or the motherboard, because with the exception of the hard drive, PSU and DVD drive, everything else has been changed. Trouble is, there doesn't seem to be a specific pattern, just random errors always referencing memory. The only thing that does seem to be consistant is that the problem always returns after I have the PC off for a long period i.e. more than just a few minutes. PSU is another option, but it is a brand new Thermaltake 450w (albeit budget) model which should be more than enough power for my hardware.

Is there anything obvious I could try? I guess these errors could be caused by either a faulty motherboard or CPU, but which is more likely? CPU was second hand from Ebay, motherboard new from Scan. I'm tempted to think it is the motherboard because in the period when it was running ok I did try a little overclocking and stress testing on Orthos and found no issues with the CPU - surely if if was that it would show up then?

Any further suggestions before I start returning things?