What is the brand and model of the PC, if it's a consumer desktop unit (i.e. Acer, Dell, Gateway, HP, ..., etc.)?
If it's not a consumer desktop unit please provide a list of the brand and model of the components used in your system (i.e. motherboard, CPU, memory, graphics card).
What type (i.e. HDMI or DVI or VGA) of video cable is being used and which port on the PC is it connected to and which port on the monitor is it connected to?