New lease of life for the old rig

[Freegs]

I am in the process of coaxing a bit of life into my old PC the stats of which were -

Windows 7
Abit IP35-pro
Q6600 @ 2.4 Ghz
Corsair dominator 2gb 1000mhz
8800gt
Western Digital blue 1 Tb

Anyway, I have just purchased an MSI geforce 650 Ti as my trusty 8800 was beginning to die (artefacts etc.). I got some new RAM as well, 2 x 2gb OCZ reaper OCZ2RPX8004GK PC2-6400 800Mhz which was sold on ebay by a computer shop who stated it was working perfectly.

The RAM caused no end of issues, freezing, restarts, no programs would run, BSOD so i've swapped it out for the mean time and am running the new 650 Ti with my old corsair dominators (great ram).

I am aware of the sensitivity of RAM, and had major problems with Crucial ballistix tracers which were initially in this build.

My question is, should I just send these OCZ reapers back or is it possible it's an issue that may be solved by adjusting timings/voltages etc. I am not au fait with this kind of I.T. meddling but am sure I could give it at go. Presumably it means going into the BIOS and manually adjusting the RAM settings. Can anyone shed any light on this, perhaps 'underclocking' the OCZ with some base settings?

I am in the process of downloading and running a memtest86 on the 4gb OCZ but would appreciate any input.

Many thanks.