Solution not working here. Dell 17" flat pannel originally hooked to my wife's (newer) XP machine. She got so frustrated with it she came into my office took my monitor and left hers. Now doing the exact same thing on my (6) yr old XP machine. All hardware is Dell. Problem so bad at times the monitor is not useable. I've wasted more than enough time on this. Close to throwing the dam thing in the trash.
I just had the same problem, it started after a power outage. The turn off-then-reset resolution fix didn't work for me, but when I removed the VGA cable from the back of the monitor, then reattached it, (power on), the message is now gone.
Dimension 4700 XP Home
Dimension 4600 XP Home (2)
Dimension XPS T600 XP Pro