Backfire Through Exhaust Now Will Not Start

This can be several things .Timing gear spun on cam or crank shaft ,timing chain jumped teeth ,distributor drive gear sheared the roll pin in the drive gear ,distributor module burned out ,if it is MSD the box may have burned out .Could be a simple as a fuel pump quit ,plugged fuel line .
First thing to do is make sure it is getting fuel .
make sure everything has power .
see if the plugs are firing .
see if you have power to the distributor .
I had a drive gear roll pin shear on a distributor once and did the same thing ,when i took of the dist. cap i could turn the rotor by hand .