this happened to my gfs box once.
depending on what you did, this might now work, but this is what i did.
create a new user
log in as that user
if the taskbar and crap loads as that user:
drop back to command line
remove the gnome config files from the affected users home directories, and replace them with the files from the new, working user
chown the files to the correct owners.
hope this gets you going, if not let us know, and mabey a greater hacker can help you.