Either the screen is broken or a corrupted firmware.
See firmware solution here http://www.satechhelp.co.za/8442/Ag-Chacer-Firmware
. See if you can access the recovery mode by turning the phone off, press and hold the power button and volume down at the same time. If you can not access the recover mode the screen or main board might be defected visit your local phone repair shop if your are out warranty.