Manufacturer Alarm

hi i recently bought my BMW 316 M reg 1994 model and the boot lock wont open so i decided to try and take off the battery hoping it would reset the lock, now i have another problem and the alarm which must have immobilizer has activated and i dont have the original alarm key so my car wont start, i know there must be a way round it as 4 weeks ago i replaced the starter motor and this happened and the mechanic fiddled under the bonnet and then the car started, please someone help me as i need the car to start so i can take the kids to school in the morning