Video Mode not supported

Ok, I know that this is a Common Question, but I cannot find the solution to fix my particular VMNS problem. There are 4 user accounts on the PC (Dell Dimension 4600) and one of the other account users changed his color settings from High to True after his icons 'had gone all out of shape'. Then, his screen went blank and the Video Mode not Supported message flashed about. The moue was inactive and the reboot in safe didn't work many times, but Ctrl Alt Del did manage to let us log on to all the other user accoutns and haveing no problem in there.
Now if the last konwn safe setup is used we can log onto the other accoutns ok but still get the VMNS message in his.
Please tell me how I can change this!!!

Start here and gl: http://tinyurl.com/gtrko