Have you tried fiddling with the boot divider? If something is pressing on that, it will stop the roof from opening.
Sometimes the microswitch gets stuck, so moving the divider (waggling it!) frees it up.
If it's not that, then it could be the wiring to the microswitch is faulty, or the motor has burnt out, or any number of more expensive causes...
www.hencam.co.uk
January 2011