Truck Wont Kick Over

I am lookin for help need to know why my truck wont kick over, lastnight i go start my truck and it doesnt even try to crank at all, let it sit for a few hrs and then it cranked right over without any problems, well today i go to sckewl and it starts no problem, commin home i stop off and get soem food, go out and it doesnt wanna crank over. The battery is givein the truck juice, the lights work and the radio, but the truck doesnt even crank at all when i turn the key all the way, Any suggestions?