0. Check if you got recent backup of your WTF dir. If not - you are most likely screwed (and should start making backups now - I'd suggest to use some RCS, but it's up to you). Backup it just in case if no backups are present (you _might_ be able to get 1-time backup from .old restored).
1. Delete Cache dir (close WoW, delete, log in back).
2. If not helped - try to replace settings file from backup or (in case you don't have it) rename .old file to replace config. I'm on vacation and don't have access to my WoW here so can't help you with exact file names, sorry.