Well Ram can cause just about anything to go wrong if its not working properly. You would need to pull the ram and try it one stick at a time and see if the problem is still there, then two etc. You need to be sure you try all differant options, if you think the second stick is bad for example try a differant one first, if it then works its most probably the stick you thought, if both seem bad try a "bad" one on its own first if thats seems ok then it could be an issue with running two. You may not find an issue buy at this point it needs doing.
Also any Overclocks you have set (GPU or CPU) may be stable at lower resolutions/workloads but when you increase the load they can quickly go from stable to oh dear whats happening.
Singling out 3dMark06, its possible you have a bad download or install. I have had issues with this before that have been fixed with a fresh download and install.