audi 80 cabriolet 1994 - immobiliser
 

I've got an Audi 80 Cabriolet from 1994, it's been standing on the driveway and not been driven for a while :(.
The car battery is flat so I've hooked it up to another for jump starting.
I think the immobiliser won't disengage and the alarm sounds when trying to start the car, also failing to start.
Any suggestions towards getting it running again?
Many thanks for replies!

--John