Im running Windows XP and have created a few user profiles (i.e. from 'user accounts' in control panel). The scenario below is when the problem usually occurs but it might just be a general fault: If one user is logged in already and you try to log in to any other profile, it just takes you back to the user profiles screen again. (e.g. if John is logged in already and you switch user and click on Peter, it will say 'loading profile settings' but then return back to the list of profiles instead) Once this happens, if you now go into the profile which is already logged in (e.g. John), a popup comes saying 'winlogon.exe has genereated an error', and then the computer shuts down with blue screen: STOP: c000021a (Fatal System Error) The Windows Logon Process System process terminated unexpectedly How do i fix this?