He's probably deleted one or more important files in error. Can the PC load in Safe Mode? If so, use this to restore all the files from the wastebin and all should be OK. Alternatively, running SFC will allow a thorough check and reinstallation of most important system files. If not, its reinstallation time. Try reinstalling over-the-top first, to retain all existing setting etc. But if this also fails, he will have to re-format C:\ and reinstall |(but first boot into DOS and save all data files on C:\ if not already secured.