Not related to AX, but since most of the times we are using RDP connections, this can be useful (I know I used it at least few times). Sometime you can get into problems with the user's profile and, at that point, the user will login with a temporary profile, which means no documents, settings, etc.
To fix this, just look at the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\ CurrentVersion\ProfileList registry key and find the key for that particular user by looking at all the keys / ProfileImagePath value which should match the path C:\Users\user_to_fix_alias. Export it (to have a backup, always do this) and delete it. Then, go to C:\Users and delete the folder as well. Note: do this from another user account, not the one you are just trying to fix.
Your user should be able to login again just fine.
To fix this, just look at the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\ CurrentVersion\ProfileList registry key and find the key for that particular user by looking at all the keys / ProfileImagePath value which should match the path C:\Users\user_to_fix_alias. Export it (to have a backup, always do this) and delete it. Then, go to C:\Users and delete the folder as well. Note: do this from another user account, not the one you are just trying to fix.
Your user should be able to login again just fine.