problem with my RAM is it faulty?

Hi, hope im posting in the right area. I have recently built a new pc around the 780g chipset with the MSI K9A2GM-FIH mobo, Phenom 9550, i also got the radeon 3450 for hybrid crossfire. The RAM i chose was 2x1GB OCZ pc2-6400 silver heatsink edition (oczp800R22GK). I installed the RAM and changed the dram voltage in the bios to 2.10volts (which is what the ram likes) and initailly all ran seemingly well but after ~4hrs it BSOD and from then on it always BSOD or no attempt of a boot (just keeps going to post). I removed one stick of ram but same prob occured so i swapped them over and now all works well with one stick of ram but the when i put the other stick in Dimm 2, 3 or 4 i get the same problem. I have since (hindsight...grrr) checked the mobo ram support and there appears to be an issue with the support with this ram although that only occurs with 4 sticks.

I have checked the temps in bios and with speedfan and these are fine.
can ram work one minute and then fault? or would the mobo be to blame for causing a fault in the broken stick?

Any other suggestions would be much appreciated as vista with 768mb ram sucks, that reminds me i have also tried turning off the internal gfx but the same prob occurs.

Thanks for reading

memtest each stick at a time at rated specs. If it errors out, bump vdimm up to 2.1v. If no luck, loosen timings to 5-5-5-15. You can find the standard timings on SPD tab in cpuz.

http://www.memtest.org/#downiso
http://www.cpuid.com/cpuz.php