Fixing Power Windows
All windows have gaskets and seals to keep wind noise and rain out. If the window has a slow spot or won't open or close properly, check the gaskets. A gasket that's misplaced or torn can prevent proper operation. If the gasket is loose, or even torn, you may be able to repair it. If the gasket is simply loose, get some 3M Super Weatherstrip Adhesive at the auto parts store. Clean off the old adhesive with lacquer thinner and reglue the gasket into place. Allow this to dry overnight with the window closed, and be certain you're not gluing the window to the gasket.
If the gasket is torn, you might be able to use a super glue to simply repair the tear. You may be able to judiciously trim a loose corner of gasket away with a single-edge razor blade. Be particularly careful about doing this on the part of the gasket that sits outside of the glass, because it may admit rain and salt spray to the inside of the door in quantities too large for the door's internal drainage system to cope with.
Replacing a gasket or seal with a new part is generally straightforward. If it's not obvious that the gasket is astray, inspect the entire gasket and channel carefully. Look for damage, but also look for such things as pine sap, fossilized Froot Loops or other foreign objects that might make the window stick or bind. Clean the surface of the gasket and window with lacquer thinner to remove oxidized rubber and scum.
There's a fair amount of friction between the gasket and the window glass. Almost any misalignment can dramatically increase the friction to the point where the motor no longer has enough torque to move the glass properly.
Lubricate the entire channel with silicone spray or protectant, because the reduced friction just might get your window working again.
It's also possible that the problem is deeper inside the door. If so, you'll need to pull the door panel and go poking around. Remember to pull the fuse to prevent amputating your fingers. You can use either a rubber wedge doorstop or a couple of feet of duct tape to anchor the glass up while you work.
Sometimes the problem is nothing more than a loose bolt allowing the door's inner structure to move around, misaligning the window track. Many doors have slotted holes for the attachment points for internal parts, so careful consideration of the misalignment will sometimes let you simply slide one adjustment a 1/4 in. or so and straighten it all out. All bets are off if the door has been damaged in a crash. It may take a long time to get everything working right.
Lastly, the mechanism that runs the window up and down may be faulty. Whether it's a gear-and-sector, scissors lift or cable-operated mechanism, you'll need to watch it moving up and down a few times. Again, keep your fingers out of the works. Sometimes the problem will be a loose fastener or rivet, sometimes a broken or missing bushing. Cables can bind on the drum or become sticky. Lube all the friction points with white grease. Don't forget there are gaskets in the window track down below the top of the door, and you may need to reglue, repair or lubricate them.