Our Mini Van is not starting. We turn the key and get nothing?

Our Mini Van is not starting. We turn the key and get nothing. The radio works as well as the lights and the windows. The car gives us nothing. We had it towed and then next morning when the repair shop checked, it started. We had the car two days later and it wouldn't start at a grocery store and it's still there. I've gone back three times to check on it but no luck.