I had the same problem twice. The first time my little sister was playing rock band and she put the guitar in wrong which screwed up my USB port on the front of the xbox. I fixed this problem by just taking a screw driver and f***ing the USB drive up even more. THis solved my problem because when the little wires were touching, the Xbox wouldn't start and when they weren't, it worked fine. THe second time it happened, I was playing my Xbox and then I just turned it of and while it was still extremely hot, I moved it to my room. When I hooked it up again, it wouldn't start. I never fixed that one, probably just over heated.