The system is being nuked as this is being written.

My buddy had a problem with a virus. AVG seemed to catch it but after the reboot, the system would not bring up a desktop. The system was setup for a single user with no password. So it should have booted right to his desktop. It booted normally up until the background of his desktop displayed, then the login screen would appear. Clicking on the user name would cause the desktop background to flash and then return the login screen.

I thought explorer.exe might have been cracked and replaced it with a copy from a good system. Didn't work.