I lost bits of KDE, here is the advice I got on Mandriva:
Alt+F2 will(/should) bring up the run window. You could
1. try running “kicker”, see if that brings the menu back so you can do your stuff
2. “konqueror”, then go to ~/.kde/share/config and delete the appropriate configuration files, returning the desktop to its default state when you next login.
Or in the command line you could simply go to that ~/.kde/share/config and delete the files that way. No need to delete everything, just stuff that is likely to affect the main desktop.