If you get to a GUI login screen and/or can login to a desktop session as guest, then I think what that's telling you is it's something specific about YOUR (i.e. admin user's) X session startup
Some common problems are (1) your user's home directory not writeable (because of permissions/ownership or disk space - I think we can count out disk space since the guest session starts OK, presumably that's on the same partition) (2) the user's ~/.Xauthority (or more rarely ~/.ICEauthority) files being unwriteable because of permissions/ownership (3) something else in that particular user's startup (possibly in an non-default .xsession or .xinitrc file or a user-specific desktop application / service)
If you can get access to the user's home dir (either by logging in normally in a virtual terminal, or from the root console) you can try to find the problem e.g.
Code:
ls -ld /home/user
ls -l /home/user/.{ICE,X}authority
less /home/user/.xsession-errors
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