Start with the right checks.
A dark display does not tell you whether the computer stopped working. Start with power, the screen and the connection. Note whether you see the manufacturer logo, a pointer or an error before the display goes dark.
What to do next.
Check that the monitor is powered on and set to the connected input. Check the cable at both ends.
For a laptop, disconnect an external display or dock when safe and check the built in screen.
If Windows appears to be running, Microsoft’s Windows + Ctrl + Shift + B shortcut can restart the graphics driver. Note whether the screen reacts.
Record what happens and whether a recent update, dock or display change preceded the problem. Use another device to view the official guidance.
Check the result.
If the display returns, save work and test the normal monitor arrangement. A temporary recovery is useful evidence, but recurring blank screens still need investigation.
Stop and get help if…
There is a startup error, clicking storage, heat, liquid damage or no response after the basic checks. Stop experimenting with recovery options if important files are not backed up.