Problems with xdm

[Adam K Kirchhoff <adamk_(_at_)_voicenet_(_dot_)_com>]

	Whenever I run X using xdm, after anywhere from 5 to 30 minutes,
the screen will blank...  ctrl-alt-backspace won't restart xdm, and
ctrl-alt-delete won't restart the machine.  None of the virtual terminals
will function and my only choice is to turn off the power and reboot.  
	This only happens on my PC and not on a Sparc I have running at
work.  Any hints and/or tips would be highly appreciated.  Thanks.

Adam