Why won't my charger charge my macbook pro?

Do you have to bend the wire to make it work? If so, you maybe just need to take a little more care of the charger...?

While charging you should keep the charger, which gets sometimes really hot, not on the bed or something similar. It can easily overheat. Also the battery could overheat.

Check the battery health! If it is under maybe 50% you should change battery. Battery become bad when they are in a hot environment. If then the battery demands to much current from the charger, the charger just overheats (transistors go mad).

If possible change the battery anyway. The maximum cycle is 1000 (according to Apple). From my point of view your battery still could have a problem.

Those battery health infos are provided by the chip in the battery. Maybe this chip (controls dis-/charging, counts cycles, measures capacity...) has a damage. This could defeat the charger. Probably... :-)

Or, you play often games which requires more power, than the ratter low power magsafe charger can deliver. This is quite easily possible and when this is the case, the charger and the battery deliver electrical power at the same time. The problem in this case is, that the only 85W from the charger are not enough to charge the battery. The charger can in this case be in the fridge, it still gets really hot... to hot maybe after some houres (when I play games, this happens as well).

Install iStateNano (free widget), it does proviede the health in percentage calculated with the max capacity. If it shows around 50%, you really should change the battery... or sell the mac :-)

Troubleshooting MagSafe adapters:

http://support.apple.com/kb/TS1713?viewlocale=en_US&locale=en_US

You may missunderstood what I wrote. The charger is dead, yes, but reaseon for it is it, what I thought we were talking about. Anyway, there is someting more that could defeat the charger: Maybe you have a unstabel powersupply in your house / flat. This would damage the integrated circuit in the charger...

lubaum: The charger will shut itself down for its own protection before that happens, as the article I linked above explains.