I assume that the back windows do not go up or down with the rear switches. If so, pop out the front drivers side door switches and check to see if the connectors are fully seated. Then check the lock out switch, it is probably bad.
Try lowering the rear windows with the front switch then bring them up with the rear. You can also check to see if the rear switches are illuminated (if equipped) this will verify that 12v is getting to the door switch.
jeff