Immobiliser how to fix?

I have a 2000 Hyundai Trajet 2.7 16v Auto, I bought it second hand a year ago and never had any proplems.
During the past 2 weeks or so a light has appeared on dash depicting an orange car together with a key which flashes for 5 seconds then goes off, at least 3 times in past 2 weeks the car has been reluctant to start. Any ideas please? as I don't want to get stranded. I live in Spain and the car gets very hot just standing outside.
The handbook says I should have a number when the car is first registerd, as I bought the second hand the number has long gone.