I am having the same problem. I've tried the suggestions and still have the problem. I tested the control panel display and it passed. I've tested the buttons and they have passed.
Using it in standalone mode doesn't solve the problem.
There is nothing in the card reader slots (and we never use them anyway).
The printer doesn't list any errors. The screen just turns dark and the "ready" (green) light and the warning (exclamation point) begin flashing.
When you turn on the power, it appears to be starting up normally, then when you see the card reader light flash, that is when the problem occurs. Is this something that can be fixed or is my printer a large paperweight now?