2011 chevy colorado loses all power when trying to start

hi guys need some help. i went to start my 2011 chevy colorado the other day and the accesories came on as soon as i tried to start it, there was a loud click and i completely lost all power in the truck. i tried replacing the main fuse in the fuse box and same thing. i disconnected the alternator and it would start up. just replaced the alternator and now its doing the same thing. anyone know what the hell the problem is? batteryhas been charged. HELP

You may be looking at a bad BCM.