It is definitely the charging cable. Although the usb tips fit they are not all the same and I’m assuming you don't have the original one. If you have a few lying around try them all. When it is charging the light will definitely flash. Also when you look at the port make sure the pin is centered. I have only two cables that will work with mine and they seem to be older. If you have to adjust the pin in the playbook use a small screw drive or something make sure it centered and keep trying different cables, the tip should fit snug around that internal pin but not necessarily around the opening.