Why won't 2000 Ford Taurus start after running pretty good?

I have a 2000 Taurus SE 3.0 Liter/ 6 Cy. After driving the car for about an hour in all the other day, I parked it and went out with a friend but when we came back the car would not start. It would make 1 click when key turned and then nothing else would happen. Electronics/ light come on fine and I also believe I hear the fuel pump turning on fine. This is only the second time the car wouldnt start, the first being during that horrible winter last year but that only lasted a day. I have been bad with getting oil changes as I'm a college student barely affording gas but try to make sure oil is in the car. I have tried jumping the car, as well as knocking on the starter(i don't know if I did it right though) but neither worked. I have even cleaned the battery connectors best I could and reattached them but still nothing. I'm in the process of finding a mechanic to look at my car so any info provided here would be greatly appreciated

How old is the battery? Its free to have it check at the auto parts store, they can check it properly with load.
Battery could only have enough power to have the lights come on, but it needs a lot to crank the engine.

Same with the starter, remove it and bring it to the auto parts store for free inspection.