2005 trailblazer LT 6 cylinder.

Yesterday I wen to start it and It turned over but wouldn't start, tried again and the. Nothing won't even crank, thought it was a dead battery so I put a different one in, didn't help. Replaced the starter relay, didn't help. Looked through all the fuses that would deal with the starter and all look fine. Starter isn't seized because when I jump the terminals it turns over. Won't let me shift out of park at all. Had it towed home ($100) out of my pocket . When I all electrical seems to work fine (radio, lights, door chime,ect) just won't crank with the key. Not sure where to look next. Any help is appreciated.