that sucks man..
try making sure all your connections are secure.
try plugging into your mobo as little as possible... like just 1 stick of ram, no optical drives.. to lighten the load on the powersupply and see if that does anything.. your powersupply seems powerful enough so i doubt this will work.. but who knows.. its worth a try. if you had a friend with pci-express comp then you could test out your vid card and all your other parts to isolate the problem..
edit: whoa i just realized this is my 800th post!
...ok now back to feeling depressed about your comp...