Ideas - you could:
1. have a look at (on GNOME) System > Preferences > Keyboard
2. check if your keyboard has been recognized (using lsdev or (on GNOME) System > Administration > Devices) (oops! you'll need a keaboard for that
- no you don't - you could copy characters for your password from, i.e., web pages)
3. log in to another session (i.e., Failsafe or Terminal) (you might even install GNOME or Xfce in order to have an alternative, graphical desktop)
4. log in as another user