This is that wonderful mystery that just happens when you least expect it, or when you are playing cutting-edge video games and your video card or software isn't setup correctly or doesn't support it.
You can know this has happened when your mouse cursor freezes on the screen, or your game locks up, and all of the keyboard buttons are dead. You are still looking at your Windows environment... but NOTHING works. The only thing that tends to work at this time is the power button...to shut it off.
You may want to try the TASK MANAGER but your chances of this working are slim.
Go ahead and shut your computer off and start it back up. Most likely it will go through the SCANDISK operation. Let it do its thing and it will soon be back in business.
A solution: it is probably something to do with your video card. Maybe you need an updated driver. You can go to the card manufacturer's web site and download it and try that. Maybe it is an hardware incompatibility issue with the software or game you are using. You might have to get a new component. Or, maybe you need a newer version of DirectX.
If this happens regularly try to lower the settings on the video card. Maybe it's your OPEN GL driver, or Resolution, or Hardware Acceleration, or driver in general. Maybe it is none of these things. When in doubt install a STANDARD VGA driver. See if this makes a difference. If it does, then work up to the freeze point from there.