Will not start

I was driving my car and it drove fine, later drove it and shut it off and would not crank back up. The car has been sitting for almost three years and cannot seem to figure out what is going on with it. I did at one point get it to start but then heard knocking when push gas, now I cannot get it to start at all. I did hook it up to battery charger for four days and nothing. I do hear fuel pump kick on and battery is good, it is getting gas, checked the pressure. I am really at a loss what to look for. I really like to get it running so I have a work vehicle because my Tahoe (which is good strong and running)is high on miles(293,750) and do not know when something might happen to it. Besides car not running it is a decent car. Any suggestions I know when it was running and heard the knock, I have been told timing. I have also been told that there could be build up in muffler. Any suggestions will help. Thanks