Misfiring, ECM

I just bought the car and now it's misfiring really bad. Three out of the six cylinders are working so I changed the spark plugs and coils still misfiring. So I bought a used ECM and put that on but my car would not start with the new one. So I put the old one back on it starts but still misfiring. I was told I needed to have the new ECM programmed to my key fob. I so know where to get that programmed. But again I put the old original ECM back on so I was able to start and drive it but it's still misfiring and now the key fob will not unlocked my car doors. I cannot get into my car now. I don't know why.