and how do i fix this...?
you might try defragging the hdd,could be that due to 5 reinstallations that the files are scattered to hell and back ??
the only other course that comes to mind is reinstall windoze right over your current setup,also see if you cannot find some video testing software,like a long movie ,if nothing else shows up,one more thing is your gfx card running at normal temps,well cooled etc,?,.:)