'96 Sidekick Won't Start

After driving for sometimes only 5 minutes, shut of the engine, go back out to leave, turn the key, lights on panel come on but - nothing - no cranking, nothing! Let it set overnight, go out and it starts right up! My wife took it to the store this evening, driving maybe 20 minutes. Ran in the store for 10 minutes, tried starting it, nothing! Boy was she mad! Can anyone help. It has a little over 100K but we have never really had any problems with it since we purchased it. Desparate!
Thanks!
It's a 4-door JX

you may need a starter

Is there any lights on when you turn the key?
It might need a new alternator. By letting it sit over night the battery will build up a charge.