The gray screen is likely the backlight. The on/off is likely a current overload.
The possibilities = start by inspecting all electrolytic capacitors for bulging or leakage. Replace any that are suspect.
Next, monitor power supply voltages to see if any don't come up to value b4 it turns off.
It is possible the backlight LEDs have a problem and are the cause even though it looks like they are coming on.