When there is no video signal reception from the processor, the monitor displays the NO SIGNAL error message. The reasons can be due to a hardware component failure, or the computer may be off while the monitor is turned on, or the cable connection between the monitor and the computer may be disconnected or damaged, or an incorrect input wire may be plugged in to the monitor. The system makes a short beep error representing an issue when the monitor is connected. The system crash prevents the monitor to display anything. The computer is now unable to boot. No signal can also be a graphics card issue. It is recommended to use a separate power supply to eliminate low power supply to the monitor.
When switching on your CPU, you can get the message No Signal displayed on your monitor, though the whole system is running. This issue might be due to several factors that you should check:
1. The cable linking your CPU to your monitor might not be properly plugged in or it might be damaged. You should ensure that the two devices are properly connected ant that the cable is in working condition.
2. You might be facing a problem with your monitor if the CPU makes a single beep error sound when you switch on the system. You can check whether the problem comes from your monitor by testing it on another CPU. If you still have the "No Signal" error displayed, including the error beep, you may need to replace your monitor or get it fixed by a professional.
3. If you receive several error beeps when starting the computer, this might be linked to a graphics card problem. You can refer to the motherboard notice or check that the connection has been properly set.
4. On some older machines there is an internal power supply for the monitor, meaning the whole system can be powered by a single cable. This setup is becoming obsolete and can cause issues with newer technology. If this is the case with your machine, you should opt for an external power source for your monitor so as to prevent overburdening it.
Note that: This problem may also be due to a failing CPU or a failing motherboard.