Follow these steps
1
Check that the monitor is powered on and set to the correct HDMI, DisplayPort or VGA input.
2
Reconnect the display cable on both ends and test another cable or monitor if available.
3
Power off the computer completely and unplug it before opening the case.
4
For desktops, reseat RAM one stick at a time; never force components.
5
For laptops, test an external monitor to separate a screen fault from a system boot fault.
6
If you smell burning, hear repeated beeps, or see physical damage, stop and arrange repair support.