Cable connections and or proper seating of the display card. Less than perfect electrical contact can do some strange things...especially when there's motion or as things expand and contract due to heating and cooling. Unplug and reseat your card and cables.
I have a win xp sp2 professional,
Here While i working in my pc every 1 hours or sometime once my monitor autometically
blok(Black color) with few millisecond its get backs to normal,
What i do?