Parts Dissapearing

'08 SP1.1
During animation Some parts dissapear..
I do not have any visibility changes set either.
Ex:
While it's animating an explode, a few parts may dissapear whilethey are moving.
Replaying the animation a few times.. Sometimes they dissapear,sometimes they don't.. And it's the parts that are moving thatdissapear..
When they dissapear, they are not visible even after i stop theanimate..
The only way to turn them back on is to toggle SW to wireframe thenback to shaded..
The dissapearing only happens in animator..

Also, When animation is stopped, If i zoom in (mouse wheel) someparts dissapear.. Zoom out a little and they re-appear..
That only happens to parts that have already moved in the animate..

What causes this? hardware prob?
See my puter specs.. Graphic driver is the SW approved..SolidworksMotion Studies