Many freezes and crashes on computers are caused by the display drivers or video subsystem. These nonresponsive states are caused by either the software drivers or a problem with your video hardware.
Many times your display driver stops responding because of driver-related issues. The best solution to the problem is uninstalling your display driver and then downloading and reinstalling the latest version.
Your video card may have a problem that is causing your system to stop responding. Your video card also may be overheating or covered with dust. Opening the computer's case and inspecting the video card and ensuring full insertion into the expansion slot are ways to identify any video-card related issues.
Your computer's CPU, RAM, power supply or AGP port may be causing your display driver to hang. Reseating RAM and CPU components often fixes many problems. If your power supply is on its way out, it may also be causing display problems. Running your AGP port at a slower speed (underclocking) may fix the problem as well.