make sure the tailgate is shut all the way, on both sides.
theres a safety switch in each latch.
also make sure all the bolts for the fiberglass top are in place.
i think its the 2nd or 3rd bolt from the rear, on the drivers side, hits another safety switch.
if that all checks out, check the fuses. then break out the DVM and check for power at the motor.
and, when did the problem start?