A lot of sunroofs (I am not sure about Volvos though....) have a manual override for the sunroofs.

The overhead center console that has the front interior lights usually can come off and have a manual slot that you can use an wrench to close and open. Obviously that is when the motor is burned out, BUT it is work a try.

Otherwise the sunroof may have come off its tracks. If that is the case, good luck, you are looking at spending some cash to have the dealer remove the interior roof paneling to fix this problem.

Hope this helps