Have you checked the fuses? In any cae you have to open the door panels. Have a look here on Johans page how to open the stuck rear door, maybe that helps.
http://bmwe32.masscom.net/
If the trunk does not open, first try some lubricant on the key and try to make it work again. In the worst case there is a way thru the skli opening behind the rear seats in the middle (at least the E32 has this). There is a perforated metal sheet which you can hammer out. Then try to climb in or use a log stick with a hood to remove the carpet cover at the rear of the trunk to get access to the trunk lock from inside.