If Completely stopped could be bad switch, bad wiring, flakey fuse, bad resistor block, or bad motor. If it works at some speeds and not others suspect resistor block. Perhaps take out motor and see if bearings are siezed up -- squirrel cage should be real easy to turn by hand. If not, bearings are shot. If you change motor you MAY have to save wiring connector from original motor as replacements sometimes come with pigtails and no OEM connector. Just my $.02