In rare circumstances, when you try to reboot from the Control Panel, the LabQuest can get stuck on the rebooting dialog.

Normally a hard reset (using the reset button) will bring it back. For detail on how to do a hard reset, see:
How do I reboot or reset an original LabQuest?

For a complete description of this problem, see:
My original LabQuest freezes and the power button does not shut off the LabQuest.