I wonder if something got screwed up in your primary account's startup scripts (.profile / .bashrc etc.)? if so, and the ssh server is still starting OK, you could try ssh'ing in with a noprofile shell
(be aware you won't even get a shell prompt!). Similarly, you could try logging in as a non-admin user and then su'ing with something other than your regular shell (and without the '-l' or '--' login shell option) e.g.
ssh yourserver bash --noprofile --norc
If neither of those work, then I think you will need to boot into recovery mode and go in via the root shell.
su -s /bin/sh adminuser