[mrlmd1]

The light still comes on because there's still some amount of "juice" left in the battery, but not enough to turn over the starter or start the bike.
Charge it up fully overnight, with a plug in charger (2 amps- not 8 or 12 or more) first, or leave it overnight on a trickle charger, before buying a new one, you may be able to recover it. If you jump it and get the bike started, the charging system of the bike is not strong enough to bring the battery back to it's fully charged capacity if it's dead. It would take a few tankfuls of gas to do that, it's got a weak, low amp output charging system. If you jump it with another battery, like from a car, just connect the battery cables to the good battery, don't have the car engine running, so you don't burn something out.
If the bike has been sitting for 6 months, there may be no fuel in the carb, so you should turn the petcock to PRIME for a minute or two, then set it back to RUN, then try and start it.