Anti theft system (PATS)

I've also had the starter replaces as well as the starter relay.

Try spare key if you have one, if not, disconnect battery for 15 seconds, with battery disconnected turn ignition key to on position and reconnect battery while key is in the on position. If this doesn't work, test battery to make sure it's fully charged to 12.4vdc, check battery cables for corrosion and make sure they're tight, check for voltage at the starter solenoid when you try to start it, if no voltage, trace back to starter relay

What is involved in starting a 2004.ford taurus