I had a similar problem with my door window but when it wouldn't go up or down, there was no way to move it with my hands.
This makes me beleive that your motor or linkage is broken.
However, a faulty switch was my problem and I took electronics cleaner to it and it was solved.
I have an older '73 450 SEL so my car may dissasemble differently but I did it myself. Patience is key because paneling takes time and its often tempting to rip stuff off thus destroying fragile retainer clips.
Hopefully someone will reply with more know-how to your problem.