It could be that one of the motors died, but it may only be a wiring issue. With the movement of the slide back and forth (or in & out) a wire may have been shorted. There are re-settable circuit breakers on many newer RV's, protecting the power feeding to the converter or other major systems, but that's probably NOT the case here since you say one motor still works.
If you can get another person to help, one can use a multimeter down below at the problematic slide motor and the other up at the slide out switch & test to see if power is even reaching the motor when the switch is turned ON. Be careful... don't get shocked or pinched under the MH.