My fuze was doing this for a few days… It turned out that the USB power cable had a kink in it. When I untied the cable and worked it back and forth to make sure all wires inside were connected, the cable began working and the unit began to charge.
It sounds like your unit is completely out of batteries. The first thing I would do to troubleshoot is find a different power cable to test it with, as a control to determine if its a battery issue, if the cable is malfunctioning, etc.