Richard, there are two motors working the z4 roof, there is one that releases and closes the roof catches and is basically located above your head behind the cover in the centre of the inner windscreen surround. The other motor is used to drive a hydraulic pump which raises and lowers the rood once the windscreen catches are released, this motor sits in a well in the nearside rear wing and is prone to failing due to water corrosion.
Normally when this motor fails the release catches will still work, so with yours not even releasing this could simply be a blown fuse or the release motor has failed. There is a worm drive connected to the motor and the plastic gear can crack and fail. Its an easy fix and there are upgraded spares available......fleabay will be your friend.