Is it a 7.3? Have the batteries load tested. They may have gone bad with the weather warming up. I was having a no start but cranking fine condition on my 02 7.3. Turns out both batteries were bad. They had enough power to crank it over but not enough to tell the injector computer IDM to fire, if the glow plugs were cycling. Turn the key to run and wait a minute and a half then turn the key to the start position to start it. It should start at that point. This is how I got my truck started until I got new batteries.