no crank no start

The starter enable relay is located under the left side of the dash, above the fuse panel.

I have a 97 Pontiac Bonneville, 152000 miles, 3.8L V-6. Most mornings it starts right up no problem. After I drive an hour or so and cut the engine off to go into work, If I need to get back out it usually won't start. Car will clunk a few times like it wants to crank, but will not. After a few tries it will just click and humm, but won't try to start. After it sits a few hours it will start right up, maybe a little hesitation but starts. It seems the longer it sits between driving the more likely it is to start.

I have had the battery, starte, and alternator tested, all test out fine. When I have this problem, there is juice to all electrical systems in the car-headlights, stereo, etc.-just won't crank.

Leaving the car running to go in a store, lunch, etc. is getting tiresome, but I don't want to be stranded. BTW-most times this happens it WILL take a jump-problem is there isn't always someone around!

Thanks for any suggestions is advance.

Remove and clean the battery cables and the positive to the starter, solenoid connection and main ground (just trace where the negative cable connects to, usually engine or transmission and a smaller ground to the chassis).