If the lid isn't opening then it sounds like the motor, or the microswitchs. The motor is situated behind the battery in the centre when you pull out the insert from the rear glovebox, if you're lucky the cables just need adjusting. If the motor has gone I would get looking for a breakers yard as the dealer price is somewhere in the region of 900 smackers.
Not really sure how best to test it though, I would start by using a multimeter to see if you are getting 12vdc at the connection to the motor, if you are and the motor is not moving then it's probably faulty (if its trying to move but not opening the hood, it's probably the cables that need adjusting). If no power, then its the microswitchs in the latches either side of the hood (in the hooks that lock the hood cover down). Microswitches aren't too dear I don't think.
You can open the hood cover manually for the meantime by twisting the motor with a socket or something. I think the instructions for doing this are in the manual.
< Rob >
Spider 2.0 TS 1997
156 2.0 TS Selespeed 1999 (now sold)
147 2.0 TS Lusso 2002