Mine did this last night, found the following procedure on a youtube video somewhere. Cant find the link because YouTube is blocked here:
1: Turn off the machine (with no disc in)
2: Turn on the machine by opening the disc tray
3: Physically force the disc tray back in with force. Not so much that you snap the thing or knock it off its runners, but enough that the motors stop retracting the tray.
The tray should stop ajar for a few seconds before the machine composes itself and continues to retract the tray.
4: Reboot the xbox and the drive should function normally.
Unsure exactly why this works but my best tech head says that the controller for the drive gets into a bit of a tizzy and doesnt realise that the laser is incorrectly calibrated. Forcing the tray this way makes the drive perform some sort of self-check in which it re-calibrates itself and works.
I tried all of the different fixes for this error that I found. There was one that finnally worked for me after hours of tinkering.
You have to take the xbox apart and remove the dvd-rom. Open this as well. On the side of the laser unit there are two tiny screw looking things. The one on the left adjusts the laser hight. I had to adjust it for about an hour befor getting the exact possition. I also scratched a game with the lazer by moveing it too high so be careful and don't use your favorite game.