Try using different usb ports. All usb ports carry 5 volts. Not all carry enough current to charge your battery. If that doesn't work try a different cord. If that doesn't work look for debris or bent pins in your charging port. Remove any debris if found. If you find bent pins there is a replacement [http://www.sparkfun.com/products/8035|here]. The replacement part requires soldering. If everything has checked out to be in good order so far. You may need to change your battery the steps for do in that are [guide|3306|here]and can be purchased [product|IF176-002|here.]