I had a Win 7 laptop in this week that wouldn't run ANYTHING. You could log in, log out, and shutdown. The registry was messed up bad so that windows didn't know what to do with ANYTHING.

After a system restore didn't work, I manually restored the backed up version of the SOFTWARE hive and everything worked. (Not sure why the system restore didn't do anything with the SOFTWARE hive.)

I'm sure the customer is VERY happy to have her laptop back in working order. She had the work rushed because this laptop WAS her business and it was great that we could fix it without having to resort to something like a Windows reinstall.