Hi,
In a other thread, Booxtor (
http://ereader-store.de) wrote that a voltage must be adjusted for the screen. There is a dependence between the batch of the device and the device's screen, so if you change the screen, an adjustment could be required...
Have you correctly plug the battery ? Have you fully charge the battery ? Have you reset the device ? What's happen when you try to shutdown the device : the blue led ?