I've just had this come up on the display whilst starting up the console. Happens within 10-15 secs of powering it on. The system is completely frozen, but no abnormal lights on the front of the xbox.
It's most likely the GPU is on the blink. It's not something you're going to be able to fix. If its under warranty then call tech support to get it fixed. If its not under warranty then youre probably out of luck. The same thing happened with one of my previous Xbox's. I'm on my third now.