Went to start it and it wouldn't start at all

Brought my truck to a mechanic he said I needed a new engine. He said he put a rebuilt but just took one from another truck. It ran for 3 weeks then one day went to start it and it wouldn't start at all. All lights on the dashboard were on. Code reader said I needed a cam shaft and crankshaft so I replace those. Put it at top dead center and set rotors correct it still won't start it starts for a second or two and then dies and won't start again after that now the motor doesn't work 5.7 everything he did was wrong. He put the valve covers on backwards and all the new parts I had on my motor are gone he gave me no information on the motor so I'm not sure if it's a 5.7. He switched transmissions from 4 wheel drive to one that four-wheel drive doesn't work. I'm having trouble getting any further information on my parts back. After replacing the camshaft crankshaft that changed my plugs and put a new rotor on still nothing. Also the code reader says that nothing is wrong. Can it be the fuel injection? I would appreciate any help you can give me.