More detailed information would certainly help. Like error messages you are getting and the Geeklog version you're on.
2_0_137 sounds like an really old version of the forum. Still shouldn't give you that sort of trouble, but the forum is up to versions 2.3.2 / 2.5rc1.3 now. See
Blaine's site for more information.
Just guessing, but if you now have a forum plugin that's only halfway installed, you could try going into your database (use phpMyAdmin or whatever you have handy) and see if you have a "forum" entry in your gl_plugins table. If so, set the pi_enabled field to 0. That should get your site back up (minus the forum).
Otherwise, see above: More details, please.
bye, Dirk