2002 Ford Expedition Engine starting

We were out driving and stopped to buy gas. After fueling up the car would not start. The battery is about a year old and the engine turned over quite fast but would not fire a single time. We call AAA and when the wrecker arrived he wiggled a few relays in the power control center and checked the fuseable link. The car then started. I noticed that the digital odometer did NOT show mileage when the car was not starting but showed "". When the car started there were actual numbers in the digital display. The next day the car would not start again. I pulled the replays and reinstalled them and now it has been starting for two days. Did I have a loose or corroded connection or will I soon be buying a new relay to replace one and which one will I need to replace?