Problem with alarm, immobiliser won't turn off

Hi, my car’s alarm which is factory fitted on s2000 and cat 1 has after 4 years of owning up decided to do a funny thing. The alarm turns on and off but my immobiliser isn’t so I can’t get it started. I don’t have recovery which is what i’m going to get now to get it towed to a shop. Anyone have any clues what could be possibly wrong with it? I’ve tried the spare key and still no joy. Cheers.