A rare fix for a problem on XP suffered by my father following a twofold issue of full C:/ drive and a powercut! When he restarted the PC it appeared that he had lost everything, and just booted up to a new plain and empty profile.
So first off I cleared out some cruft using C-cleaner and got 1GB of space back, then moved a load of installation files to some redundant space on the PC and got back another 500mb.
Then to restore his profile I headed into: My Computer (right click) > Properties > Advanced tab > User Settings. This brings up a dialog listing the user profiles available on the PC. I identified his original profile which had been labelled back up and the new profile that had been created when he restarted. Tried to delete this new profile but couldn’t. So into Control Panel > Users and created a new user with Admin rights. Logged out, logged into the new user and went to user profiles and deleted the new profile for his main system. Logged out and logged back into the main user and thankfully his profile returned. Then deleted the newly created user account.