2000 Expedition, 72K miles, 4x4 - runs great, however after it's turned off for 30 - 40 minutes, it won't start. Nothing happens. It doesn't make any noise at all. The dash lights & radio go on, but car won't start. If I wait 15 - 30 minutes, it fires right back up. Of course it didn't do it for the mechanic who had it for 5 days, but did it when I got home. Battery is fine. Any suggestions? Thank you so much!