I tried jumping my truck but it won't start, I broke the plastic shifter, it is an automatic, i also tried tapping on the starter, I think it might be engaged in a gear still not sure though. Please help.

 

Year make model engine please.

Won't start can mean: cranks (turns over) but won't fire or won't turn over but clicks or nothing at all.

What is yours doing?

I know there can be more crap with automatics (like if you aren't in P it probably won't start) so there are probably more things that could be causing this but the things to check when your truck won't start are SPARK, FUEL, COMPRESSION. Spark and fuel are the most common culprits. Narrow it down to which of the integral components needed for an engine to start is the one you're missing, then trace what's causing it to be missing.