A while back I acquired a 97 cobra rolling shell . It did not have a key but I needed to move it so I just drilled out the ignition lock so I could steer it around . I decided after some dreaming and a little research I would rebuild it , found a cobra engine , a ECM , a complete wire harness a a whole bunch of other parts. Little by little it all came together, then I got back to the ignition pulled a lock and keyfrom a local U-pick and just assumed it would start right up ( did not know anything ) . Theft light flashing , no crank , ....all the symptoms... Finally I called a locksmith out of mesa to reprogram my key to the system , he ran program, re-keyed the door locks and cut a second key and programmed it , then he explained how the key was not matched to the ECM and how the PATS would react . Flashing theft light was done , car started right up never saw problem again. So all that said , my question is , where did key #3 come from? Who programmed it ? Could this be your problem ? Try removing it , then try your original key . Hope this helps sorry for the run on story.