Random crank but no start

Bought a car off of a car lot in Brownwood, Texas about three weeks ago. After two weeks of having it I left work went in the store came out and it would not start and it would not start for about four hours. It is done it a few times since every time I have got it back started. I am blessed with the fuse box underneath the hood mainly the fuel pump relay because there is a single black wire ran to it that is going back to the wiring harness at the back of the car underneath. I am guessing it is the fuel pump, but it is wired information. Also, my feet fuse box underneath hood when wiggled turn the lights on and off all kinds of stuff.