must keep mouse moving or video stops and computer freezes?

i've read post on this subject for weeks, maybe months, none of the things posted have solved the problem: when downloading or watching most videos, it all stops until i move the mouse? this does not happen with my laptop, or any other computers i have tried: just this HP desk computer, running windows 7
one laptop runs windows 7, the other XP: but both are running thru the same dsl/router line.
thanks