0403jacqui

Hi - I am new to this but here goes. I purchased a 1998 slk230 with vario roof. It has developed a problem over the last two days in that the roof will not close properly. It opens fine and folds into the boot but after using the car for a period of time when I come to close it the windows go down and the boot lid opens but the roof will not move. I can hear the motor trying to move it but nothing. I have left it over night with roof down and in the morning tried again and the roof closes no problems. This has happened twice now. I have read on here some older posts that mention a problem with some micro switches? Can any one tell me where these are located and how to replace them?
Any help is greatly appreciated. Thanks