If your PC doesn't have a separate Graphic's card and your monitor was connected to your Motherboard's Video Outputs using your processor's IGPU then you disabled your video output to your Monitor.
Temporarily install a GPU card and connect your Monitor to it and then enable your IGPU again in Device Manager.
If you have Windows 10/11, Restart your PC 3 times when it starts to boot into Windows. By the 3rd time you should see Windows Diagnosing your PC in which then a menu will pop up. Select Troubleshooting Menu and restore your PC using a Restore Point earlier before you disabled your IGPU.
OR Run the Windows Installation setup and click on "Repair this computer" or something similar. Then use the Troubleshooting Menu use Restore Point to restore your computer before you disabled your IGPU.
You can also try to enter Windows "Safe Mode" and then enable your IGPU again.
