Cranking but won't start

My car started running hot. Heater wouldn'twork either. My boyfriend replaced the water pump and the 2 themostats. He drove it down the road it didn't get hot. He shut it off and went to start it back. Wouldn't start only crank. So he replaced the crank senor wasn't it. Checked the plugs. It's getting fire. The fuel pump is coming on. He also took the air mass senor out still wouldn't start. I took it to mechanic he's had it for a week. He still don't know either. But keeps telling me he'll have it fixed the next day.