My zen battery was low. I charged it for about 5-6

My zen battery was low. I charged it for about 5-6 hours using a computer. The device showed docked. When the battery was fully charged, i disconnected the device. The unit still showed that it was docked although it was not. The docked symbol stayed on for a long time. I gave up and went to bed. The next morning the device was blank. I can not get it to turn on or do anything. It was fully charged according to the battery light.