Okay so I own a 2004 Jeep Grand Cherokee Overlander, just got it and the battery is fairly new and this happened twice, the engine doesn't turn over all the lights turn on and the radio goes on but i just don't know whats wrong

 

clean up battery ground connections

 

It doesn't take many amps to turn on the lights or run the radio. It takes a lot of amps to turn over the engine. Do as above, clean all your connections. If this does not improve the situation, have your battery load tested. You may have a cell or two dying in the battery.