2001 Mitsubishi Eclipse 01 Eclipse won't turn over unless u

2001 Mitsubishi Eclipse Automatic

Okay please bear with me, I'm a chick who knows nothing about cars, but I'm trying to outsmart my bf who thinks we can't fix his car ourselves. His car keeps cutting off then won't turn over (or stay running for more than a couple seconds) for about 1/2 hour. The computer thingy at AutoZone said something about the rear O2 sensor, but my bf changed the front sensor instead and the car drove ok for a while with check engine light coming on sometimes while idling. The other day while driving I turned on the A/C and within minutes the engine cut off while I was still driving. About a 1/2 hour later it finally turned over again. Hours later we tried to start it, but the engine wouldn't start till my bf unplugged something I *think* was the front O2 sensor. Now about 95% of the time the engine won't turn over unless he unplugs that part. Do you have any ideas that I can claim to be own? LOL!