I don't have the debian installation but here's what I recommend:
1. Build a set of "emergency rescue" disks. Don't worry, your system isn't
in an emergency but it's a good idea to have these disks anyway. They are
a boot disk and a root disk and you can down load them from
ftp://sunsite.unc.edu/pub/Linux/distributions/slackware/
Find an appropriate bootdisk in the subdirectory bootdsks.144 and
get rescue.gz from the rootdsks subdirectory. The Readme files tell
you how to make boot disks and root disks.
2. Use these two disks to boot your system. Mount the linux partition on
the harddisk as /mnt . Make sure, you know, what partition that is, before
you screw up the hard disk. You can check with fdisk if you are not sure.
3. You are now master over the linux partition. Go in /mnt/etc and edit
the file inittab. Modify the runlevel, so that linux does not run X
at boot up but that you get a number of text terminals. Consult your
linux book or post your inittab file, so I can tell you what to do.
4. After successfully changing your inittab file you should be able to boot
from your hard disk normally and get a number of text consoles.
5. From there you can try to fix the problems. It sounds like X was not
happy and died prematurely. From a text shell you can try to call startx,
which in turn will give you all the error messages.
Good luck
Rudi