It sounds like you need to install the correct graphics driver. Your PC will use a graphics card (even if it is an on-board card) to produce the image on your screen. If the correct driver for the hardware is not in use you may see odd results like the ones you have mentioned. Search for drivers for your PC. (You may need to search for the name of the Graphics Card in your PC first.)
Install the driver and make sure that the display settings (resolution, colours etc) are set as before.
Huw CA, January 2005