after heating up van doesnt start for 2-3 hours?

I have a 1996 dodge caravan le sport 3.3L I am at 168,000 miles. when running, van is a champ but...lately when i go somewhere, I come back out to start it and nothing...I have lights, but I usually sit for 2-3 hours then it usually starts up again, and runs smooth until i get to where I am going More
I have a 1996 dodge caravan le sport 3.3L I am at 167,000 miles. when running, van is a champ but...lately when i go somewhere, I come back out to start it and nothing...I have lights, but I usually sit for 2-3 hours then it usually starts up again, and runs smooth until i get to where I am going and same thing happens..this started when I would use the electronic door locks...after about 10-15 min the alarm would go off so now I manually lock it but this other started. Sometimes when I go out to start it it will not start (after it has sat over night) I am a real dummy when it comes to cars and this really has me baffeled! any ideas?