Suddenly today my truck will not crank. It turns over fine but doesn't fire. It's like the plugs are not firing or something. What could cause this? Plenty of gas and oil. I tried spraying starter fluid into the intake and it still didn't fire.

 

There are many causes of your problem. Many times it is the crank sensor. Are you getting a check engine light? Using a code reader will lead you in the right direction to solve your problem.