1997 vw jetta security system

While sitting at a stop sign my jetta shut down completely and the alarm begam blaring. after about 5 mins. it stopped and began again as soon as I inserttd the key or opened the door. My driver's side door lock doesn't work (the whole thing just pulls out) and the pasenger side lock won't even turn. I towed it to a mechanic who said that if the bsecurity system came when new they would have to replace it but if it was installed later they could override it. Is this true? And do all 1997 jettas come with a security system? I know the original owner d
added some things and the security system may have been one of them. I don't want to get ripped off. I there anything I can do to correct it myself? Thank you for any help. .