Hello Peter
My name is Dayarys.
Go to safe mode and see if the problem continues:
https://support.microsoft.com/en-us/windows/sta...
If the problem continues, it could be a video cable or the monitor; Otherwise, it could be the graphics driver, in that case, download it from the manufacturer's page according to your model and install it.
Let us know if you need more help.
Sincerely,
Dayarys