The “No input signal” message can sometimes appear if the POST process is failing, and the computer cannot boot properly. If the POST process is failing and the computer is not starting up, the motherboard could be at fault.
What does input signal not found mean on HP monitor?
Typically, a monitor displays a message “no signal error” when there’s a problem such as a loose cable, loose connections, or a problem with the input device. Graphics driver and output resolution problems can also cause this error.