I have some experience with the 240 and 760 sunroofs. Both in manual
and electric models there are two corkscrew gears in the frame and the
crank or motor places a single round gear between them. As the small
round gear turns it causes the corkscrews to turn and wind a notched
work gear through and drag the sunroof along its track. So if you
loosen the mechanism enough for it to drop out a bit and disengage the
round gear (either removing the manual handle or uncrewing the motor
from the roof and letting it drop out or, better still, removing it
completely) you will be able to see the two parallel corkscrews.

Now the roof should slide more easily when you pull it open or closed.
At that time you can observe the gears and see if they turn when you
are manually dragging the roof:

1. If both corkscrews turn you are in luck and it is likely that the
motor was not in tight enough and was just slipping.

2. If one corkscrew turns and the other doesn't then you have a
snapped cable. On the 240 this was the single most expensive repair I
ever had, almost $600 CAD, almost all labour cost.

3. The third possibility is that either the screw(s) or the drive gear
are stripped (possibly due to condition #1 left unattended).

Although pulling the roof shut will not pop it up in the back to sit
fush with the roof, it will keep regular rain from coming in while
you're parked as it should drain via internal channels. BUT if you
drive with it like that then any water in the system will empty out on
your head during sharp braking or cornering (my wife and I had to wear
towels on our heads once while driving home in a hurricane).

Hope this helps. This first diagnostic steps are among the most
end-user friendly jobs because everything is accessible and you can
sit in the driver's seat whil you work.

Good luck!
blurp