96 Windstar anti-theft problem
 

Just bought this car and after 1 day it decided i was an intruder and my only key wont turn the ignition at all. I can lock and unlock the doors with it, and the KES and RES lock and unlock the doors fine as well. i've done that many times and still when I put the key in the igniotin the anti-theft light starts blinking again and it wont turn. any ideas?