There are at least two or three freeware memory checkers out there - google memtest (one I found a while back).  I'd try one of those to rule out the memory.  Whwre'd you get the memory from.  The modules I got from Crucial have a lifetime warranty IIRC.   What is now Microsoft's anti-spyware got rid of cool for me when even the specialized cwshredder wouldn't, so if you have CWS, I'd try that but I don't think it would be causing all those problems.

I'd strip the box down carefully, remove and reseat the memory module and all the cards and make sure any socketed chips are seated - they can work loose over time.  Check the fan(s), make sure it's not overheating.  You might also try running sopme other freeware diagnostic programs.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken