|First, you can do it from a power switch. They have safeties built into them to prevent you from shutting a computer down accidentally. Just hold the power switch for 5-10 seconds and it will turn you computer off.|
Second, it sounds like you either your graphics card is failing or your power management is turning your monitor off too soon. To know for sure answer these questions:
Does the monitor turn off while you are using the computer or when your computer is sitting idle for a period of time?
Are any of your cooling fans making squeeking or buzzing sounds?