What screen size is your player, 320x240 or 220x176?
You need to get your player into update mode and use ConsumerUpdate to flash the correct firmware for your screen size.
What you need to do is this,
1) Switch the player OFF using the main on/off switch.
2) Hold down the menu key and keep it held down.(may be a different key for you, can be Play key or Volume key, but there are only 5 to try anyway)
3) Connect the usb to the player.
4) Wait for about 10 seconds before releasing the menu key.
5) You are now in upgrade mode
6) Then just connect ConsumerUpdate and upload a working firmware.
ConsumerUpdate should also REBOOT the player before starting the upgrade.
There are some Rockchip Firmwares to try in the downloads on this site,
Looks like a DEC A780
DECA780
DEC Downloads