I'll echo the response that System Restore is what you should do. That is the easiest and fastest way to go about it. It sounds like some environment variables got trashed, or that files got pruned out when they shouldn't have. Do a System Restore, and also try getting a command prompt running in admin mode, and then run SFC /scannow. If all else fails, try to do a system repair from the install DVD. If that still all fails, you might also try posting over on official Windows 7 RC Support Forum (located here http://tinyurl.com/9fhdl5
) to get a response from the Microsoft devs. They will probably want some more in-depth information on your equipment and build-out, so I would prepare that as well.
Kurtis Whittington - Microsoft Windows Client Team