Will not start and throwing codes

Okay, my name is Julie. I just bought the car took a few seconds to start but started it drove fine until it overheated. I noticed the fan was not working so went to auto zone got fan switch sensor changed it, filled it with coolant and drove about fifteen or twenty minutes fixed the problem. So I thought once I got to my location it sounded as if coolant was boiling but went about my business when I went to leave car would not start, it sounded like it wanted to but would not. So had it towed home had a few people look at it and they could not figure it out. The gas gauge said half tank so I checked fuses everything so I got more gas just encase put it in turned the key on and off a few times and then started it and it started let it idle. Then took it for a ten minute drive and was sitting at a long light and looked down and boom it was almost on the red. I panicked went ahead and drove the half block home and parked it well their was water in the oil I think blew head gasket. So two days later started it up went one block it wanted to go when I wanted to stop brake was hard to press went back parked it. Got bars head gasket repair put right amount in and now will not start. Throwing code p2074 p0513 p0685 p0688 for the p0513 I figured out that my PT Cruiser's key was on the same key ring removed it re keyed it only threw the three other codes. Now I am stumped and overwhelmed. Please help