Cut the wires if you are willing to replace the regulator
 

Want to 2nd what was said above. It is likely the wires have jumped the pulleys and are jammed. If you are willing to replace the regulator, just cut the steel wires which will mechanically disconnect the window motion from the motor. If the wires are really jammed, you may have to cut them in a couple of places.

They are about as hard as bicycle brake cables. Hardened steel side cutters can cut them. Electrical wire cutters will not...

Thanks guys for the replies. I was a bit busy, but I will take a look today. I will try to unbolt the motor regulator first. I know I can access those bolts.
If I need to cut the wires, aren't the wires behind the window?

cutting cables
 

You should be able to reach the steel cables (just to be clear - not the electrical wires!) once the door panel is removed - even if the window is down.

I had to do the exact same thing on my X5 about a month ago.
I put in a Dorman regulator that has been fine so far - it was about $75.

If you are able to unscrew the motor, test that it goes forward and backward so that you know the switch and motor are working. If the motor only spins one way, the switch is the likely culprit. You can put a volt meter on the motor leads to check that if you get that far.

After you cut the steel cables, you can slide the window up and block it up with some wood, zip tie it, etc., to make it weathertight until your new regulator arrives.

Fixed it. It was the central console button. P/n 61316902178.
What happened was one side (when opening the button cluster) was broken and made steady contact, so the window regulator motor was spinning in one direction only: down. The regulator was OK, as well as the window motor.

I will post some pics in a few days. I did the autopsy of the switch, and put it back together, so the car can be used.