Grey display upon boot up

Does it complete the first 5 steps fo the boot phase?  Do you hear the test sound? If so, you probably have a display issue.  

• Check cable connection is secure at both ends of the display flex cable.
• Check cable connection is secure at both ends of the backlight inverter cable.
• Replace complete Front Bezel Assembly

If it's not the display I would look at the API or main board.  

Boot Phase Boot Phase Event

1 Switch the monitor on using the On/Off switch. (Green power light is lit as soon as the device is connected to AC mains.)

2 The green AC Power LED blinks for about during the boot phase.

3 You hear a ‘pop’ from the loudspeaker.

4 Green AC Power LED stops blinking, and remains lit.

5 Boot Screen with the Philips Logo appears on the display. Test Sound is issued. .

6 Boot Screen with the Philips Logo disappears. Fixed screen elements (for example smart keys, alarm fields) appear on the screen.

7 First measurement information appears on the screen, touchscreen is functional.