You might just try the window controls forty or fifty times. May just be rusty. I had a similar problem on my '81 300SD with the driver's seat. So much so that I removed the seat, turned it upside down, and hooked the motor up to my battery charger. For some reason it just started working again - I actually did nothing to it. Put it back in the car and it has worked for another six years or so.

So it might just be due to inactivity.