'94 e36 320ise window/sunroof problem

Hi Hoping someone can help. My car has developed a really strange problem with its electric windows/sunroof. Occasionally the window/sunroof system just plain won't operate! I have noticed lately that in particular if I switch the car off & restart fairly quickly it won't work for at least a couple minutes. Anyone know a reason for this?? It only started recently & has never happened in the past. Central locking system works fine. If it helps at all The system is only on the front doors & roof (rear doors are manual winders) and the one touch system only on the drivers door.