I have had this same issue. Its not complicated at all. Its dirt and wear on your contacts in the switch. If the switches are lighted, its not the fuse. Take the switch out, take it appart and clean it with alcohol. If its wear related, put the down switch in the up side, and the up switch in the downside. It looks wrong but it will be on the clean contact side in the switch and your windows will work again. There is a write up on how to take the switches apart on e30.net.