Windows on the BMW 330i refusing to go up and down are fairly common to the model. Unfortunately, it can't be easily said that the cause are bad BMW 330i window regulators. There are other possibilities to consider whenever you are having difficulty with the glass. It can either be an electrical problem or a mechanical problem on the regulators themselves. To be certain that the issue revolves around the BMW 330i window regulators, there are a few steps you can take to isolate this as the only problem. Try these out first before you commit waste money to buy replacement parts.
For power windows that work via a switch, the problem might be electrical in nature. There might be a blown fuse, a cut wire, or a damaged circuit. If you are certain the wires and other electrical parts work, it's one step closer to isolating the window regulator. A good way to check if electricity is moving across the car is to try and turn on other electrical devices: radio, air conditioning, interior lights, headlights, etc. If these work, you are at least assured that your components are powered. Try operating all switches to move the windows. If all windows fail to move, there may be something wrong electrically.
New motors are available and are less expensive instead of the complete window-regulator assembly. A running motor should make a discreet hum when you turn the switch. If you try to adjust the windows and you don't hear anything, chances are you have a stuck or busted motor.
You may have a motor of the BMW 330i window regulator that's running, yet the window still doesn't move. On the occasion that it does move, it may not be reliable enough to work all the time. These points to a problem in the other parts of the regulator: the lifter, cable, or runner. Open the interior door panel to have a full view of the part. You may find these parts in question to be already damaged. Now you can be sure that your BMW 330i window regulator needs a replacement.