[Druchii]

Create a new user profile then, rename his account folder while logged in as Administrator.
This is found in C:\Documents and Settings\ (on XP)
Or: C:\Users (Vista)

Then, try logging in on the account. It should then be as simple as copying across any missing data (Pictures/music/Documents etc...)
Some programs may need to be configured again also.

Repairing the profile itself is pointless, not even sure if it's possible.