To repair a malfunctioning power window on a car, start by evaluating the corresponding switch on the door panel. Many power window switches can be pried out of their fixtures using a sharp object such as a knife. Try not to scratch or damage the door panel upon removal. If this doesn't work, it may be necessary to remove the door panel to access the switch.
Once the switch is removed, use a voltmeter to check its voltage with the ignition switched on. If there is voltage, the problem could be in the switch or the power window motor. Use a jumper wire to bypass the switch and deliver power directly to the motor. If the motor operates, this means the switch is bad, so replace the switch. If nothing happens to the motor, it's the motor that's bad, so replace the motor.
If the switch has no voltage when checked with the voltmeter, the problem could be in the wiring between the fuse panel and the window switch. Visually inspect the wire connections for signs of damage. If no damage is present, try moving the wire while pressing the switch. If the window suddenly works or works intermittently, this shows that the problem is in the wire. See what you can do to improve the connection or replace the wire completely.