ok first off what EXACTLY does your xbox do when you turn it on? i.e. flashing red and green power button, no video, reboot? if it has the "your xbox needs service" in like 10 different languages then you do have an error code in the upper left hand corner.
i wonder if a hotswap would work...
@fsg ya i saw that too its basically a demo that updates the dash but he has to be able to cold boot xbox games.
try booting your xbox with a game in the dvd drive. if it boots then you could try this. otherwise your prob gonna have to go with a hard mod.