This could be caused by an old flash. Back in August 2011, Microsoft pushed one of the huge dashboard updates which reflashed/updated the firmware on xbox consoles. If you didn't restore your stock firmware before updating, it corrupted the firmware. From what I've read, it's a pain in the ass to recover; basically impossible for most LiteOns, BenQ, and Hitachi.
As said in above posts, it may simply be bad cables. I've had that happen to me before.