If the screen on your device is frozen, try holding down the power button for 7 seconds. A menu should come up that will allow you to select an option to restart the device. If the menu fails to pop up, try manually restarting the device by holding the power button down for 40 seconds.
If restarting the device doesn't cause the screen to change at all, the screen itself may need to be replaced. Before you decide to replace the screen, make sure to double check that there are no problems with the battery, because the battery will be less expensive to fix than the screen will be. If you are sure that the problem is not with the battery, go to the Amazon Voyage device page and follow the link to the Screen Replacement repair guide to learn how to replace the screen.