what is the hose hanging of the backnod my 2008 Ford f250 truck. on the exaughst side

*Hands-on* inspection / evaluation is going to be required.

This hose probably doesn't have anything to do with your troubles. If your anti-theft light is not blinking while attempting to start the vehicle, and your fuel pump cut off (inertia) switch is not tripped, have testing performed for engine performance to find out why the vehicle will not start.