trigger

I have a 1996 ZX 1.9D estate. In June the electric sunroof packed up without warning - I closed it on leaving the car, came back two hours later - not working. it has not worked since - at all. It's not the fuses; my garage has checked these. When these things pack up like this without warning, is there a commonly experienced reason? I'm wondering if I can investigate the prob myself, rather than have the garage strip the roof down to find it. Has anyone else had this problem? Thanks