voyager 3.3 won't start
 

Hi, I have a chrysler grand voyager, it's 20 years old but has only done 72 k. in the last couple of months it won't start. the battery is fully charged. I think it has someting to do with the alarm system. i have been in touch with a main dealer but becourse of it's age they can't carry out any dinostics. the key fob opens the doors and seems to switch off the alarm, the car starts for a couple of seconds then stops. it would be a shame to scrap it. anyone any idea's.
Cheers Danny.