help! just upgraded and now can't login!

[Tim&Pep <amugbmug@pacific.net.ph>]

Hi,

I'm a Debian newbie. I have just used apt-get to upgrade my system and
now I can't seem to log in at all under X. I can login on one of the
other virtual terminals (or whatever you call that when you press
ctrl-alt F6). What have I done? Can I fix it? Thanks.

Tim