Patient: "Doctor, it hurts when I bend my elbow like this."
Doctor: "Then don't bend your elbow like that."
In other words if something specifically is giving you trouble, stop doing it. Obviously you need to fix whatever the problem is (and as a hint, it is probably not a virus, so you can stop that anyhow for now). It seems fairly clear to me that the problem is hardware related. If replacing your RAM hasn't helped, move on. Have you tried a different power supply? If not try to do so, as was mentioned earlier this could be your problem too. If you don't have or can't borrow one, disconnect all extra devices (optical drives, extra fans, lights, etc). Basically run bare minimum hardware and see if the problem is resolved or not. If running with minimal hardware fixes the issue, replace your power supply. If not the RAM, and if not the PSU, you can check your hard drive for damage, though this is not likely to be the problem. After these things, I would say replace your motherboard.
\Dan