This problem generally occurs when you install a new monitor. To fix this issue you can try reinstalling the monitor once again. Below find out what you need to do:
Start the system in Safe Mode. To start PC in safe mode, reboot the PC and while PC reboot press the F8 key continuously. The system will display the Windows Startup Menu, choose Safe Mode from the option listed in the menu and press Enter. Now click Start, right click on My Computer, go to Properties then Hardware tab and then click on Device Manager button. Now click the Plus (+) symbol located next to Monitors entry to expand it. You can see the installed monitor (s), select it and click on Uninstall. Now exit the Device Manager and restart your PC. This time your Windows will reinstall your hardware automatically.
Or else you can visit the manufacturer official website and manually install the required drivers on your PC.