Won't start after stopping for gas

My Prizm has a rebuilt engine. Its check engine light was on and it had trouble running cold. We ran a scan tool on it. And it said misfire on all cylinders and random misfire and that there was something with camshaft position sensor.I had been driving off and on pretty much all day and at the end of my trip I stopped to get gas. I shut it off filled up and it wouldn't start again. We replaced the fuel pump and it started up. I drove it home. Went to start it the next day and it won't start again. We replaced the camshaft position sensor but that didn't help. Still won't start. Any help would be great. Thanks