My computer(macbook air) seems fully charged but wont work when you unplug the charger what do I do ?

It seems like the article you cited above is pretty complete with recommended steps.

One thing to look at is this: When you have the machine plugged in and working, does the power indicator in the menu bar show pretty close to a full charge? (If you don't see the power indicator near the top right of your screen, go to System Preferences > Energy Saver and click "Show battery status in menu bar".)

Under the Apple in the Menu Bar About This Mac > More Info... > Power what does it tell you about the status of the battery?