I'd check fuses, then the switch connections, and then maybe you'll have a better idea if it's a bad switch or something else.
That's probably the direction i'd head in then, you might have something as simple as a bad connection. It could have corrosion on the plug, a loose connection, or it may be a windows switch that's faulty. I'd take them apart and check, and make sure you check both sides before swapping out switches, as it might have a bad circuit causing the failure (one side being disconnected). You could try some CRC Contact cleaner spray on them even, it's designed for cleaning electrical connections and is safe to use on them. I know Advanced Auto Parts carries it, and most other places should as well.
