99 mustang security wolnt let me start
 

Lately my 1999 3.8 mustang has been acting weird. When i jump in and try to start it the 'theft' light will flash and when i crank it, it just turns over. And sometimes when i let the key sit in it for a min or to i turn it to pre start (lol) and the theft light will be solid, and the motor will start right up. Ive disconnected the battery for about 5 min, tried a spare key, and thats bout it. Any suggestions? Thanks!!!!!:smashfrea