Take the highest probability guess - a stuck motor.

Not unlike the flat-rater approach for disassembling front ends, beat on it.

With the ignition on and the switch held in the direction you wish the window to move, take the flat of your fist of your other hand and smack the inside door panel in the approximate area of where the motor is. If you don't know the exact location, try various places.

The harder you smack, the more likely you are to free it.

Be more conservative in your whacking of a concours restoration...

Good for diagnosing.
Good for getting a stuck-down window back up in a downpour.

If this has no action, you are either

a. not smacking hard enough or
b. have a switch/connection problem.

Note that if this does get the window moving, you still have to repair or replace the motor. (Neither does turning up the radio permanently fix a rod knock.)