Help asap!!

I have a 2008 Escalade with no power whatsoever. nothing in the Escalade works not the remote lights nothing. the truck won't even a lock with the remote or with the button inside the truck. the truck won't even turn on nothing works but the AC and the navigation. last night I was sitting in the truck with the stereo on and the key out of the ignition. I open the driver's door to open the passenger door got back into the driver seat and nothing would turn on. no lights come on nothing but the AC and navigatio. I had to get it towed to my house last night please help. I think it has something to do with the anti theft system.