Read through http://support.apple.com/kb/TS1713 and make sure the connectors are all clean and appear functional. As an additional note, there have been a number of users with problems from using knock-off chargers and cords. They are not always made to the proper specs. You might consider taking your MacBook to an Apple store genius bar and have it checked with an Apple charger to compare with your charger.
Im having a similar problem with my charger. At first it would only charge in a certain position and then not at all. no cuts but it stopped charging and the battery has gone flat. Does your battery still hold a charge without being plugged in?
Some basic fault finding suggests its the power pack/cable and I have an appointment at the mac store today Ill let you know if its something other than that.
Also you can get the life cycle of your battery checked to see how much life is left in it.
I would never opt for the cheaper knock offs as they are usually cheap for a reason including the adaptors and iphone chargers which i had a couple and they only lasted a few weeks.