A. As you have tried replacing the monitor and yet the problem continued you can change your VGA cable and check if it continues or open the chassis and reaffix the Video card if you inserted it loose and try to check the display and if still the problem continues you need to upgrade the video card driver to the latest version available and check the display in the Safe mode if you find the same result or try to change the PCI slot of the Video card these may truly help you out if not it related to the driver and you need to update the driver and if you don’t know the model of the Video card just type on the Start button and select the RUN command from the start menu and type dxdiag in the Run option and click ok you will get the entire information relating to hardware as well as software or else go to device manager and you will get the specification relating to the Video card. And even after installing the latest driver the problem continues you need to replace the Video card.