Do the lights etc work? If not check if there is a current between the battery terminals with a multimeter. If nothing try charging again, if still nothing try another battery. If there is a current make sure all the connections in the wire are clean, check there is a current getting to the starter motor, maybe try connecting directly from the battery to the starter motor to see if that works (make sure you're out of gear of course!). If there is charge in the battery and its getting to the starter, and its a case of the starter is just not doing anything then take the motor off, clean it, test it, if still nothing then replace.