My windows 7 starts up fine desktop loaded then in a matter of seconds, the screen goes black and I have one little white square that looks like either a shrunk desktop page or some other page. Not a solid white square, definately something shrunk to the corner. If I go in safe mode, same thing. If I do ctrl alt delete, where your choices would be to bring up task manager are outlined with colored boxes but no words and background still black. I have hooked up an external monitor with the same results. I work on computers on a daily basis and have never seen this. Please let me know if you have any ideas for me.
If you have a spare graphics card you could try swapping out the graphic cards and see if that solves the problem. Did you make any changes (install new software, adjust the resolution, or any other changes) before this started happening?