Door won't close, alarm goes off.

This is killing me so I would greatly appreciate any feedback or suggestions your could give. My wife borrows my car and I come home one night and she says the door won't close. So I go out to the car and I can't get the door shut. It's like a little bar has dropped down and prevents this from latching. It seems like an anti-theft mechanism because now if I open the door the alarm goes off. I can get the door shut but you have to jam it a lot. When I go to start the car the alarm goes off again and it just won't stop. Is there something that can be reset like disconnecting the battery and re-connecting? I'm frustrated as hell because I can't go anywhere and everytime I get in the car the loud ass alarm goes off which wakes the whole neighborhood! Any suggestions/advice would be greatly appreciated.
Thanks,
Dennis