Make sure the monitor is plugged in and powered on. If it’s powered on, there should be a light on or near the power button and you should get an error message such as “No Signal”.
Most monitors have a button that lets you choose between the different monitor inputs. Check that the input source on your monitor is set to the same connection as the cable you’re using (HDMI, DVI-D, or Displayport) using the correct button on the monitor.
Confirm the display cable is plugged into the DVI-D, HDMI or Displayport ports on the horizontal graphics card and not the vertical HDMI port. The onboard ports on the motherboard (top left silver bracket) will only work with a CPU with integrated graphics chip. The exact layout of your PC may be different, but generally you will want to plug in the monitor cable to the graphics ports that are below the green, pink and blue audio ports.
Confirm that the monitor cable is plugged into the monitor output port, not the input port if any. Some monitors will be able to send a display to another device, but that same port will not be able to receive a display from the computer.
For any following steps, please make sure that the computer is off and unplugged.
Re-seat the graphics processing unit (GPU), and RAM modules:
To re-seat the GPU, first check the back of your case and see if there is either a sliding bracket with 2 screws, or a single hinged bracket with 1 screw. If you see a bracket, you will need to loosen that screw and move the bracket in order to expose the GPU screws. After you have moved the bracket, or if your case does not have a bracket on the back of the case, open the side panel (usually glass) and remove the screw(s) mounting the GPU onto the bracket on the left side with a Phillips-head screwdriver. Press plastic tab on the right side of the motherboard slot that the GPU is inserted to in order to release the card, with your finger or carefully with the screwdriver tip. Once the card is released, slowly rock the GPU back and forth horizontally towards yourself to remove the GPU. Reinsert it, making sure it is firmly secured. You should hear or see the plastic tab lock back into place. Reinsert the screws and close the bracket if necessary.
To re-seat the RAM module, first open the side panel (usually glass) that you can see all of the components. To the right of the CPU cooler, there should be one or more vertical sticks. These sticks are the RAM modules. To remove them, check to see if there are locking tabs on the top or bottom of the slot that the RAM module is inserted in. Press down on the top and bottom slot (if applicable) to release the module. Then, insert the module back in the slot, one side at a time, making sure that the center notches align correctly and that the locking tabs on the top and bottom (if available) snap into place. We find that it is easiest to slide the module in the bottom of the slot first, pressing against with your thumb it until you hear it snap into place, and then press against the top of the module. Whether you have one or two locking tabs, you still should hear 2 clicks when inserting the module into the slot, one for each side.
If you have more than one RAM module, check each one at a time in order to isolate the defective component. You can also re-seat a single RAM module in a different slot to see if the original slot is the culprit.
Ensure that the CPU power cable (black or black/yellow) on the top left of the motherboard is inserted securely by removing it and plugging it back in. To make sure that it is plugged in correctly, there should be a clip on the slot and the plug itself. Confirm that these plugs are lined up.
Take the CMOS battery (silver coin) out, wait a minute for it to drain and then reinsert it into the motherboard. Here is a helpful guide from Intel.
If your monitor uses a port that is not on the graphics card such as VGA or DVI-D, you may need to use an adapter. For VGA specifically, you will need an ACTIVE adapter to convert the digital HDMI, Display Port, or DVI-D signal to an analog VGA signal. An active adapter has an additional cable to receive power, usually from an outlet.