pcm not communicating

Hello - First time posting. I need help with my '00 v6. some background: I started having some trouble with starting it last fall ( having to let it crank a few times before it it would start). I put it away for the winter, putting a battery tender on to keep it from going dead. Fast forward...

So I bought another mustang as a project... it's a 1999 v6 5-speed ford mustang. The car will crank but won't start. Also the fuel pump doesn't kick on. Theft light is flashing, and the pcm is not wanting to communicate to a snap on tablet. I first began to replace the fuel pump and filter, and...