What makes a video memory, or graphics card, run out of memory?

When I play Shogun II total war, it freezes in 15 or 20 minutes, but when I play Empire total war, it freezes in approximately 5 hours.

and an error message shows up saying "run out of video memory".

I don't know what causes it, and I would appreciate any help.



I have nvidia gtx580 installed.|||That doesn't sound right because the GTX580 should play those games with hands down no problem. your card might be defective. I recommend you contact Nvidia about this.