I have had problems with this before and the only way I saw to solve it was to go out and buy a new charger. They are expensive and they run from about $90-$110. Here is one that will work with a variety of different laptops at a very reasonable price. If this doesn't work then it is probably the piece that is built into the laptop that the charger connects to. Hopefully that is not the problem.
Here is the link for the charger.