Quick answer
When the monitor stays black, first check that it is turned on and that the correct signal source is selected, then inspect the cables and their connections. If there is still no picture, check whether the computer is actually running (fans, lights) and if needed check that the graphics card and RAM are properly seated.
How to recognize the problem
- The monitor is completely black, but the power light is on
- The screen says "No signal" or "Check cable"
- The computer can be heard running, but there is no picture
- The picture occasionally drops out or flickers before disappearing
Most common causes
Faulty or loose cable
The monitor power cable or video cable (HDMI, DisplayPort, VGA) may be loose, damaged or incorrectly connected.
Wrong signal source
The monitor may be set to the wrong input (e.g. HDMI 2 instead of HDMI 1) or automatic detection is not working.
Graphics card not properly seated
If the graphics card is loose in the slot or lacks power, the computer will not send a picture.
Faulty or insufficiently seated RAM
Poorly seated RAM can prevent the system from booting, so the monitor stays black even though the computer is running.
Motherboard or power supply failure
A damaged motherboard or insufficient power supply output can result in no picture.
Step-by-step fix
- 1
Check that the monitor is turned on
Press the power button on the monitor and check that the light is on. If it is not, check the power cable and outlet. Try another power cable if you have one.
- 2
Select the correct signal source
Find the input selection button on the monitor (often
InputorSource) and select the input the computer is connected to (HDMI, DisplayPort, VGA). If you are not sure, go through all available inputs. - 3
Check the video cable
Turn off the computer and monitor, then carefully unplug and reconnect the video cable at both ends. Make sure the cable is fully inserted into the port. If you have a spare cable, replace it.
- 4
Connect the monitor to another port
If you have a dedicated graphics card, make sure the cable is connected to its output, not to the output on the motherboard. If the graphics card has multiple outputs, move the cable to another port (e.g. from HDMI to DisplayPort).
- 5
Check that the computer is running
Listen for fans and check whether the light on the case is on. If the computer is completely dead, the problem is with the power supply or the power button (see our guide on that).
- 6
Reseat the graphics card
Unplug the computer from power and remove the power cable. If the computer is under warranty, do not open the case. Before touching components, use an anti-static wrist strap or touch a metal part of the case. Open the case and carefully remove the graphics card. Check that there is no dust on the contacts and that the card sits properly in the slot, then push it firmly back into the slot and connect any additional power if present. Turn on the computer and check for a picture.
- 7
Check the RAM
Unplug the computer from power and remove the power cable. If the computer is under warranty, do not open the case. Remove all RAM modules. Put one module back and turn on the computer to check for a picture. If there is no picture, try another module in another slot. If the picture appears, add the remaining modules one by one, turning off the computer and unplugging the power cable before each change. The module that causes the loss of picture is faulty or poorly seated. Make sure to put the modules back in the correct slot.
- 8
Test the monitor and cable on another device
Connect the monitor to a laptop or another computer using the same cable. If the picture works, the problem is with your computer. If it does not work, the problem is most likely with the monitor, the cable or the output on the other device.
- 9
Check the graphics card power
If the graphics card requires additional power, make sure the appropriate PCIe cable is properly connected. Insufficient power supply output can lead to a black screen.
If nothing helps
If you have gone through all the steps and the monitor still stays black, there is probably a fault with the motherboard, graphics card or power supply. In that case, it is best to take the computer to a repair shop or call IT support. Do not try to repair components yourself if you have no experience, as you could cause further damage to the device. Also, if the computer is under warranty, do not open the case so you do not lose the warranty.
How to prevent it
- Regularly check that the cables are properly connected
- Use quality video cables and do not bend them too much
- Clean dust from inside the computer to prevent overheating
- Avoid frequently removing and reinstalling components unnecessarily
When to call a professional
If you have checked all cables and signal sources and the monitor still does not show a picture, or if the computer shows no signs of life at all, contact IT support. A professional can quickly diagnose the fault and replace the faulty component.
IT infrastructure maintenance · Servers, networks, backup, security and helpdeskFAQ
The monitor is black, but the light is on. What does that mean?
The light is on, which means the monitor has power. The problem is most likely with the video cable, the signal source or the graphics card. Check the cable and select the correct input.
How do I know whether the problem is with the monitor or the computer?
Connect the monitor to another computer or laptop. If the picture works, the problem is with your computer. If it does not work, the problem is most likely with the monitor or the cable.
Is it safe to open the computer case yourself?
If you have experience, you can carefully open the case and check the connections. Make sure to unplug the computer from power and remove the power cable first. If the device is under warranty, do not open it. If you have no experience, it is better to call a professional.