I think a proper diagnostic would be helpful before proceeding further.
First, does your Beosound's door motors run when one waves their hand in front of the unit?
If not, the power supply to the door may be out. The control board controlling the door motor may have been taken down with it.
If the motors run, does the motor run continuously? If so, it's most likely the belt which is attached to the door gear mechanism. It probably runs continuously because the limit switch for the door isn't being actuated - the belt might be too loose. Of course, it's a good idea to check this limit switch to see that it is working properly.