Monitor showing no signal: cables, input and display settings

A monitor that shows a no signal message is actually on and working. It just isn't getting a picture from the computer. LG sums up three main causes: the wrong input setting, a cable that is loose, damaged or incompatible, and a PC that does not respond.

The monitor's power light helps confirm this. According to Dell, a solid white or green light means the monitor has power and is receiving a signal. An amber, orange or blinking white light means the monitor has power but is not receiving a video signal, and Dell calls this a computer or cable problem, not a monitor fault. If the light is off completely, the problem is the monitor's power, not the signal. Light colors differ between brands, so match them against your monitor's manual.

A monitor with several ports, such as HDMI and DisplayPort, only shows the picture from the port that is currently selected. LG's steps:

1. Find the monitor's control button or joystick. Depending on the model, it sits at the bottom, the back or the front of the screen.
2. Press the button or joystick to open the main menu.
3. Select Input.
4. Choose the exact port your PC uses, such as HDMI 1 or DisplayPort.

This mistake often happens after the monitor has been moved, its cable replaced, or has been shared with another device, such as a game console. With two monitors, LG writes that the monitor showing no signal may have the wrong input selected or a loose cable. Swap the cables or ports between the two to see whether the problem follows the monitor or the connection.

1. Unplug the video cable completely, at both the monitor and the PC.
2. Check the cable ends. LG asks you to look for bent pins or debris in the connectors.
3. If the connectors look fine, plug the cable back in securely at both devices.
4. Use the original cable that came with the monitor. LG strongly recommends it, because a cable that does not meet the product's specifications can cause display problems.
5. If the problem continues, try another compatible cable. Microsoft writes that if the new one works, the old cable was faulty.

Microsoft also warns about display splitters. A splitter only duplicates the same signal, so it cannot make two monitors show different screens. If the PC has only one video port, a second monitor needs a docking station or a USB-C adapter that provides an extra video port.

A desktop PC with a separate graphics card has two sets of video ports on the back: ports on the motherboard and ports on the graphics card. Dell writes that the graphics card ports are usually lower on the back panel, and the monitor cable should go there. Using the wrong motherboard port is a common cause of a no signal screen, especially on gaming or high-performance PCs.

In Indonesia, many desktop PCs are self-built or bought as custom builds with an added graphics card. On these PCs, the motherboard ports often stay visible even though they are not in use. LG gives the same rule: connect the monitor straight to the graphics card, and only use a motherboard port if the PC has no separate graphics card.

If the monitor only works on a motherboard port, LG says there may be a problem with the graphics card or its driver. Microsoft also suggests trying another video port if the PC has more than one, such as HDMI, VGA, DVI and DisplayPort.

A monitor also shows no signal when the computer has frozen and stops sending a picture. LG gives a simple test: press the Num Lock key on the keyboard several times and see whether its light turns on and off. If the light does not respond, the PC has probably frozen. Press and hold the PC's power button to force it off, then turn it back on. LG warns that unsaved work may be lost.

Dell suggests disconnecting non-essential accessories such as external hard drives, USB devices, printers and VR headsets, because they can interfere with startup. Keep only the keyboard, the mouse and the monitor, turn the computer on, then reconnect the other devices one at a time to find the culprit. Microsoft gives similar advice for laptops: remove any connected docks, dongles and adapters.

For a laptop connected to an external monitor, Microsoft asks you to press the Windows logo key and P, then make sure the Extend option is selected. Other options can leave the external monitor without a picture.

If the monitor suddenly shows no signal on a setup that used to work, try these steps in order:

1. Press the Windows logo key, Ctrl, Shift and B together to reset the graphics driver. Dell writes that you will hear a short beep and the screen will flash briefly, which is normal.
2. If that does not help, restart the computer.
3. If the problem started after a Windows or driver update, roll the graphics driver back to the previous version. Open Device Manager, expand Display adapters, right-click the graphics adapter, choose Properties, then Roll Back Driver if it is available.
4. If that option is missing, Microsoft suggests reinstalling the display driver, and Dell suggests downloading the latest graphics driver from the computer maker's website.

Microsoft suggests trying the monitor with another computer to find out whether the problem is the monitor or the computer. The result of that test decides where to take the equipment:

• If the monitor still shows no signal with another computer and another cable, take the monitor to its brand's authorized service center. LG also offers further support and technician visits for LG monitors.
• If the monitor works on another computer, the problem is the PC. If the graphics card gives no picture while a motherboard port works, have a computer technician or the PC brand's service center check it.
• If the monitor's power light is completely off, follow the steps for a monitor that will not turn on, then take it in for service if it stays dead.
• If a pin is bent or broken in the port of the monitor or the graphics card, do not try to force it straight.

Do not open the monitor case. Inside is a power supply board connected to household power, and any work on that part is a job for a service center technician.