I had a similar problem with my rear driver side window.
1) Took the door panel off and removed the foam covering.
2) Tested the electrical connection to the motor. Got + and - 12 V when pressing switch up and down.
3) Removed the motor. Got continuity across the leads. Hooked the motor back up to power, and it spun strongly in both directions when activated.
4) Reached in and moved the window up and down manually to make sure it wasn't frozen or off the track. Window moved freely.
5) Said "screw it", reinstalled everything to see if it worked. Window started to work again just fine. It's been working fine for about 3 months now.
ETA: Once the door panel is off, removing the motor assembly is very straight forward. Carefully remove the foam lining from the forward part of the door. Unplug the electrical connection from the motor. Test to see if you get (+) and (-) 12 VDC across this cable when the switch is in the up and down position to ensure the motor is getting power.
The motor assembly is held on by (3 I think) screws that are easily accessible once you remove the foam lining. These screws connect to what I would call the black plastic "gear box" on the lower part of the motor assembly. The screws are parallel to the deck and perpendicular to the drivetrain (basically point out toward the side of the vehicle). The silver motor winding is held onto this gear box by four small silver screws; don't mess with these. The screws holding the motor assembly onto the door also hold the cable winding that is attached to the window to move it up and down (this black plastic spindle assembly is sandwiched between the inside metal of the door and the black motor assembly.) Be careful removing these screws and the motor, because this black plastic cable assembly seems like it could come apart easily, and your cable can get unspooled.
Now you have the motor out, hook it back up to see if it works o.k. You can also reach in and move the window up and down, ensuring it moves pretty easily, and also carefully ensuring the cable assembly rotates clockwise and counter clockwise freely.