Starting problems

My car w ill not start.
Previously I have taken out the battery, charged it all the way up, then tried again, even putting it in first gear and cranking. One time that worked and the car worked perfectly for about one week. Lets say twenty start ups, then suddenly nothing again. Only cranking. The starter was a bit stuck yesterday, I heard the click when I turned the key. So I pushed the car to some speed, and clutched it into first, letting the motor turn half a turn, then the starter was free and it started right up. Then today it would not start again. It cranks, I have checked the spark plugs, they give a nice strong spark, and are clean. The spark plugs where also moist with petrol. What more does it need?