No start no crank

When I go to start it I can turn the key and nothing happens no clicks nothing all my lights come on and so do the headlights. I cannot pull the shifter out of park either. It was doing it every now and then and all I had to do was unhook the negative side of the battery for a few minutes and it would crank. But now it will not do anything at all. Need it fixed as soon as possible as it is my only ride right now. Also, it has been skipping and has a rough idle. We replaced the spark plugs and checked the coils and the coil boots all is fine it has a new battery in it bought in March of this year and a new oil change done. I have had people say it could be the computer or a wire or the shift sensor because it seems like it is not registering its in park. If it does turnout to be the computer how do I go about programming it for my truck?