I had disappearing desktop icons, something got stuck on the screen once and the printer disappeared. So I took out the memory (4 sticks), sanded the contacts with printer paper, shuffled them and put them back in. No probs since.
I used to have some 90% alcohol but they don't sell it at the local store anymore. I should find some. My next step would have been to clean the memory slots with alcohol and a toothbrush.
If you have more than one stick (you should for dual channel mode), you can try removing one/half to diagnose problems with the memory itself.