Windows XP user name changed to USERNAME.COMPUTERNAME, now account is back to defaults

Solution 1:

Classic case of a corrupted profile. Many ways it could have happened. If you don't want to delete the profile reg key, you can try changing the ProfilePath Value of the

HKLM\Software\Microsoft\Windows NT\Current Version\Profile List\<SID of User>

Key back to the original folder, but be forewarned that in my experience this rarely works. Instead it's best to delete the entire SID, backup/delete the profile folders, and reboot the machine. When the user logs back on they'll get a fresh profile, and you can manually copy the data that's needed back to the 'new' profile folder.