A reg file with the following content can save you from a black screen:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Contro l\GraphicsDrivers]
"tdrLevel"=dword:00000000
But what should I do if I have Windows 7, and when I open the file, I get an error message saying "editing the registry is prohibited by the system administrator"?