Here are a couple of possibilities.
The shade on our SOB started acting just like yours.
I could pull it down then use the switch to move up
. Found the learning switch
but also found a wire that the shade had been rubbing on and cut
A quick fix with a soldering iron and some heat shrink
If your chassis battery has been replaced or drained, your shade will/may have forgotten where to stop. It should stop at the top, dash and if the mh is running about halfway down.
The "learning" button mentioned by Pete'sMH is used to teach the shade where to stop.
Hope it's an easy fix and let us know.
Edit: here's a thread with programming instructions.