There are several possibilities. I'd start by attempting to more the roof with the emergency nut in case the clutch in the motor is shot.
Mine was glued to the seal and the lifting angles were broken, some parts were missing, and the bridge was twisted. Still not finished with it, as I need to paint the edges of the roof panel and install some more bits.
If you can move the sunroof with the emergency nut, you have a motor or clutch problem. The gears can break, leaving you with no movement of the cable. Replacements are available -- search "sunroof" and you will find several sources.
If the nut turns, but the roof doesn't move, you will have to pull the headliner down and find out what is wrong. It clips to the front of the sunroof, about 2" back from the front edge, with four "christmas tree" type clips -- use a putty knife or similar to pry them apart and slide the headliner back if you can. (I'm assuming that there is a liner under the sunroof, I'm not sure what is there if this is a smoked glass type!).
The liner (standard type) is a large panel in front, a narrow panel in back, and two side rails that are behind the headliner. You can bow it down and CAREFULLY pull it out -- if you bend the side rails too much you will have to replace it! It normally comes out from the top, which I would advise if you can get the roof even partway open.
More details if you need them -- see some of the other sunroof threads.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!