2002 Dodge Caravan wont start after been driven for a littl

The starter dose not work the lights an radio come on but the starter dose nothing I can hear the relays clicking and the emerg shut down realy gets hot I switched the horn relay to that spot and the van started got me home I went to parts store and got a new relay in staled it and van would not start lights and radio come on but no action from starterremoved the battery put on charger and checked all wiring to starter and every ehere under the hood I could see and feel did not find any loose or other problems with wiring about 2 or 3 hours put battery back on and starts right up?

I carried it to the shop tuesday evening and left it. The van would not attempt to crank for them wednesday morning after checking it all out the mechanic said he thought it was the computer (brain) this was replaced under extended warinty in march of 2009, the machanic acted as if that was just a guess and was not sure what was wrong?