What is wrong with my computer?

Man that sucks, such an awesome system and that happens. My advice is to get 1-2 GB of ram, remove all of your RAM or one at a time to see if ones had it. Every issue you said it had kept making me think it was the RAM. Have you tried taking out the RAM and put it back it, It could be "Component Creep" meaning that they have become a little loose, that happened to my heatsink. Anyway, I hope this helps because that's a very nice system.