I have a win7, 64 bit Dell inspiron pc and occasionally the image on the screen just shears into numerous horizontal strips of various vertical widths.  some times you can see remnants of the task bar at several different levels of the screen.  If I have an active window open from the internet it usually is intact with a little shaking and as long as I don't have to click on anything outside the window I can continue to work with it while the parts of the screen that I can see are useless to me.  When this happens, I can sometimes see enough of icon to click on it but usually as I near an icon with the mouse pointer the pointer skips left or right or disappears.  I usually have to turn it off manually, though some times it just clears up on its own.