It could be due to a dirty, corroded dock connector, broken pins on the dock connector, or a bad power management IC as well as multiple other issues. I would suggest you try one thing at a time. The toughest part of these repairs is the trouble shooting. You also want to plug it into your computer and see if your computer recognizes it etc. Best place to start for a decent trouble shooting is a new battery. It will provide you with a known good point, and go on from there. Hope this helps, good luck.