Issues with bmw 1997 coup trunk oppening

you should be able to tip the rear seat you should be able to trip the lock but check for a release cable around the rear deck, much easier

You can get back into the trunk, this is tricky but i have done a few times use the key in the trunk key hole and turn key one way all the way and then turn the other way while slightly lifting on trunk.

try it a few times it is tricky but trunk will open, there is something about the way the lock is set up due to it using battery voltage to open it, but with out battery it is funny, do not give up, turn key all the way both ways, the key will turn a little further to the left i think to open trunk. good day. let me know the out come.

Your linkage to open the door in disconnected , the lock assemble will need to be removed for the solution

http://www.bmwe34.net/E34main/Trouble/Locked.htm

here are many solutions.

Search the BMW forums like Pelican Parts or DTM Power or United Bimmer Community. When I read of problems with convertible trunk lids, a common suspect is a failure in the system that won't allow the trunk to open when the roof is down.

if the doors and trunk are vacuumed operated, make sure all the doors are unlocked..this might make it easier to open the trunk..or get the car running and then try to open the trunk with the car running..turn key all the way to the left and push slowly in..I think it is vacuum operated like the mercedes

I vaguely recall reading something in the owners manual of my '97 328 regarding the trunk and the master key. Something about locking things with the master key so that valets cannot open your trunk with the valet key.
Try unlocking the driver door or the trunk with the master key (the original key that had the LED flashlight in it.

On the side of the smart key there is a mechanical key that slides out of one of the sides-There should be a little release lever retaining the mechanical key. It can be inserted into the trunk lock and turned to open the trunk. There are several other positions the key can be turned to place the trunk lock actuation in different modes- it should be in your owner's manual Hopefully I have been helpful

if you have a newer 07 and on, there is a lock cylinder near the trunk grab handle. you will have to kneel down to be able to see it. the mechanical key thats inside the remote will have to be used. a spare/valet key wont work. support your local bmw dealership

i believe that your trunk is unlocked and to prevent damage the system locks it self, check the trunk.
lock it with your key then try it out.
that happened on a audi cabriolet and we locked up the trunk and problem solved. let me know if that helps, if not i will try something else