I have something weird happening on just 1 of these: at random times (meaning I cannot duplicate the problem at will) the monitor will go completely black ... except for the cursor. I can move the cursor around the screen just fine. The hard disk does not seem to be doing anything abnormal (meaning I don't think there is anything running amok in the background).
The power settings are set to "maximum performance". Sleep mode and "Turn monitor off" are both set to "never".
Hitting alt-cntl-delete does not bring up Task manager (or maybe it does - I just can see it).
Powering the monitor off then back on doesn't do anything.
After messing with a bunch of things, unplugging the monitor from the back of the computer brings the picture back - but at the lowest possible resolution (the user normally runs at maximum resolution).