This is a similar problem to my mouse freeze of a few weeks ago and only occurs when I am using the Internet.
After the machine has been left on for a while, when I scroll down using the mouse wheel, the screen goes black for a few seconds. If I scroll in Word or Excel it's perfectly fine. The only answer is a reboot, but does anyone know why this should happen?
Edit: Once this problem manifests itself, it will happen every time I scroll until I reboot.