Well, do you hear any clicking when the switch is moved? If not, then perhaps it is the switch. I believe there is also a harness connector going into the door that can something have a bad connection.
You might want want to just try pushing down on the window a bit to see if that unbinds the motor gear. Sometimes they will just stick at the top. From what I understand, there is no stop limit switch on the windows on the C5. So the motor forces the window up to the top till the control module senses that the motor is drawing too much current and then tells it to quit.
Sounds like a silly way to do this, but that's what I have read. Sounds like an excellent way to quickly burn out window regulator motors.