Please do not suggest seeking a professional.
I've owned this 1997 Mitsubishi Galant for 4 years.
All 4 power windows have worked, up and down, until today, April 2, 2012.
Yesterday I opened the left rear door to place an item in the car. I then locked the car.
Today, I notice the left rear window is all the way down.
I do not remember using that left rear window, when I was driving the car on Saturday.
The left rear door panel is still off from a power door lock repair. I'm thus able to see the window mechanism and check all the connectors.
There is a window lock button on the left front door. It does not seem to work. Whether pressed in, or not pressed in, the other 3 windows still go up and down.
What can cause one power window to fail to function for the first time ever, since owning the car?
Like I said, I do not remember using the left rear window the last time I drove the car. When I need some fresh air, the left rear window is the last one I consider, because air in that window heads around the back of the car toward the passenger side. When I want air on my side, I use the right rear window.
Is it mechanically possible for this window to have gone down with the doors closed, the key not in the ignition, and me, the owner, in my house?