Need some help
 

72 K5 Blazer 350/350

I was cruising down the highway and all of a sudden I heard a loud backfire and immediately lost power. Coasted to the shoulder no problem. Visual inspection showed a blown out muffler but no other visible damage. Lights and acc. work, but the engine wont crank. What the Hell happened? Has anyone else ever had this happen? Thanks in advance.

Capt. Dave