Help! Distortions on screen appear when using internet or Windows Office

Hi,

I have a strange problem with my Gateway LCD monitor. Whenever I
start using the internet, or Windows Office applications, images on the
screen will distort periodically, usually 10-15 mins after. The images
appear severely stretched, flicker, and have horizontal lines running
through the screen. However, when I switch to desktop, everything
returns to normal. Would appreciate any advice on troubleshooting this
problem. Thanks!

– JS