what would cause the engine to not crank

sorry, no work was done, i got off work. started fine when i went to work. like when the battery is dead it goes click,click,click. this is just 1 click

well,if the battery is fully charged/good and all connections are clean,tight,free of corrosion,then get a helper and a hammer(sounds bad don't it)have the helper try and crank/start the car while you tap/smack the starter with the hammer.if the starter attempts to spin or spins the engine,then the starter is bad.