Have a 2000 Alero. drivers window won't stay up, falls down.

your window has fallen off its track. either remove the inner door paneling and re seat it on the track, or take to mechanic. It is a cheap repair.

Forget it. You've got a broken window regulator. Have to replace the entire unit.
Replace window regulator Ricks Free Auto Repair Advice

The glass for your window sits on a metal bar on the window regulator assembly. The bar is raised by scissor like lifts run by a motor. If it falls forward the rear portion may have come off from the bar and the guides at the rear may have kept it from lower along with the side that is still attached. You will have to open the door panel to gain access to it. Inspect also the guide for dirt or it may need replacing, it could have caused the part of the window to come of.

Below is a sample of what the assembly would look like:

http://aq.ioffer.com/i/96-97-98-99-00-chevy-cavalier-window-motor-regulator-98879862

If you can hear the motor running while pressing the window switch you may have a broken clip or something in the way causing the window to slip off track. If no sound comes while pressing the window button you may need a power window regulator motor "OR" the window button itself may need replacing. If the window was down when it stopped working and had to be manually rolled back up, this can cause the glass to randomly fall back inside the door. This is because the car thinks that the window is still down and will continue to fall until it tells the computer that the window was closed using the power window button. If the window falls at just the wrong angle you could end up having to replace the glass as well.

it is the regulator and one can be purchased at your local automotive parts store. More then likely the will have to order it

Since you hear the motor, it's probably the cable connecting the motor to the regulator, but the cable itself is not replaceable. The regulator and motor come as an assembly.

This site sell parts and give you step by step instructions along with tools needed for window regulator replacement. Took me 2 hrs last weekend. copy link below it will take your to part needed.

http://cpwstore.carpartswholesale.com/catalog/?N=0&sv=0&VN=4294967189+4294966242+4294965810+4294966811+4294967010&Ntt=Replacement+Window+Regulator&Nr=AND%28universal:0%29&ref=partfinder

It probably did not fall off. There is a plastic piece on the regulator that can break if in a bind. When this happens, the window just falls into the door. You need a new regulator/motor assembly for the door this happend on. Dealer is expencive. Napa will have it for $120.

probably worn out regulator,especially if you haer the motor when you press the button,try various nissan wreckers it should be $100 maybe $200 but thats it labour should be 1 to 2 hrs depends on mechanic,definately window reg problem

Hi my name is Allen!

When the window falls down it is because the cable for the regulator and motor broke. The only fix is a new regulator/motor assembly from the dealership, or a good one from the junk yard if you can find one.

For further asistance you may reach me at FixYa!