Engine turns over but will not start

Was raining pretty hard Monday, around 4:00 PM ran through high backed up water on the street twice. The second time, it was so high, my fan belt squeaked a couple of times as I went to my destination. Went to a few places that day. When trying to leave around two AM, my van would turn over but would not start. Sounded like no fuel or fire but had to get a tow home. Later Tuesday evening a pretty knowledgeable truck mechanic came by to help. He tried to start it several times but no. Got out his diagnostic tester but could not get the tester to link up with the van. After many attempts, putting more fuel in the tank, he started checking several fuses. Still no. Unplugging the battery post and allowed time to reset. Still no output readings on tester, no instrument readings on the dash and no radio. The power slide door (passenger side door has a ramp for Handicap) and interior lights worked fine. He Called his friend who worked at the Chrysler dealership repair shop but could not reach him and left a message to call back. He suspects the ECM might be bad. Two days go by and no response. As I am writing you, I go outside to verify everything my friend said was going on. Wow! The van starts! Any Idea what has Happened? I am Handicap, I need to trust my vehicle not to leave me stranded.