alarm system lock my 98 van to start

I have this 98 town and country with this problem since I buy it. The alarm system act like if I were stolen my own van. I do all I can do to disarm it but nothing works. I have to wait some times hours, some times days or weeks. I hope somebody can help me on this. thanks.

Wish I knew enough about the alarm system to help you. When you disarm it and try to enter does the alarm go off?