Hi WingTransport,
If you have an electric motor driving the slide, it probably gets power from the row of 12V DC mini-circuit breakers near the battery.
If the other slides, probably hydraulic, are working, the buss bar with those breakers should have enough power to drive the electric motor.
If all the slides are dead, you may have a tripped manual-reset breaker on that buss bar. If tripped, the battery won't get charged and when you go to use the slides, may not have enough juice to drive the high current devices. There's a teeny-teeny-tiny reset button on one of the breakers. The breakers are near the battery, and are usually covered by red rubber boots.
If everything else is working, you may have a wire that's come off from a wire nut near the motor, or perhaps a motor failure. Sometimes that wiring is under the bed platform. Sometimes behind the fascia. Perhaps another 4200 owner knows and will chime in.