Try that, and once you get it working again I would also run some general tests (such as memtest) to make sure your PSU didn't hurt anything (since it was the only change you mentioned, I am assuming it might be a problem). You really should run a test on your HD (if it is new-ish it has soemthing called SMART which reports a bunch of values for diagnostic purposes). I beleive the program speedfan can conduct such a test. Also check your voltages (using motherboardmonitor 5 or speedfan) and make sure that they are around what they should be and don't fluctate