Laserjet M506dn does not begin initializing when powered on - display is black, all 3 LED are lit up

[CreamyBeige]

I have an m506dn printer at work that does not finish initializing when turned on. It just sits with a black control panel screen and all 3 LEDs are lit up and stay that way. I have tried turning it off and on again, unplugging it for a little bit, leaving it there. It never goes beyond a black screen. I cannot select cold reset because the control panel does not switch from black. To be clear the control panel is LIT black, it is not "dead" black. I have linked a picture of what it looks like below. I did not see a troubleshooting step for this on HP. 

Any ideas?

https://ibb.co/PFT3c8L


RESOLVED EDIT: 

I removed the control board panel on the rear left side (it slides off). This is the panel that is just to the left of all the inputs and outputs (ethernet etc). I reseated the connection of the screen to the control board and this seemed to resolve the issue. 

[CaineThePaine]

Hello here are some steps to try for troubleshooting your printer. First thing to try is the little button located on the back of the control panel. Repeatedly pressing the button cycles through the available diagnostics. A pen or pencil can be used to press the button. This tells you if the control panel itself is working.

During normal operation, cooling fans begins to spin briefly after the printer power is turned on. Place a hand over the vents in the right- and left-side covers. Lean close to the printer to hear the fans operating. If the fan are operating, the dc side of the power supply is functioning.

If the fans are operating correctly, the next troubleshooting step is to isolate print engine, formatter, and control panel problems. Perform an engine test. If the formatter is damaged, it might interfere with the engine test. A.Remove the formatter. B.Use a small pointed object to depress the test-page switch located on the rear of the printer. (NOTE:The test page can only use Tray 2 as the paper source, so make sure that paper is loaded in Tray 2.) If the engine-test page does not print, try removing the formatter, and then performing the engine test again. If the engine test is then successful, the problem is almost certainly with the formatter, the control panel, or the cable that connects them. (NOTE:Depressing, and holding down, the test-page switch causes the printer to continually print test pages. Releasing the switch stops the test page continuous printing.) (NOTE:Operational fans, motors, and control-panel lights indicate the following:-AC power is present at the printer.-The power supply is providing either or both 24 Vdc and 5 Vdc voltages.-The DC controller microprocessor is functioning. If the engine test page prints, the print engine is operating normally (a failed engine test print page does not necessarily indicate that the print engine or DC controller is defective).

Hope this helps, thanks.

[CreamyBeige]

Thank you for taking the time to respond. It ended up being the cable from the display to the control board. Reseating that resolved the issue. 

[CaineThePaine]

Your welcome, and glad you were able to figure out the cause of your problem. Hope you have a great day!