If my car turns over, why won't it crank?

check engine light on?if it is,what is the engine code?NOT good to run the car low on fuel.that is what keeps the pump cool and working properly.if the fuel pump is not covered by fuel at all times,it gets hot,works harder,and will fail!when the gas hand gets to 1/4 tank,consider that as EMPTY,and go put more fuel in it!