I've just installed some sort of relatively old video card and now computer freezes while playing certain video games (Civilization 4, HOMM V). Some other video games with far better graphics works well (Dawn of War I). Note that "freezing" games run nicely and smoothly for about 10-15 mins, no lag or any other indication that video card may be not good enough. And then PC suddenly freezes, nothing works but rebooting.
The question is, is this a normal behavior of a video card which is simply "not good enough" for the games in question, or is there something broken? Card itself or motherboard or whatever?
OS is Windows 7 if that matters, and I don't know exact videocard specs but that probably doesn't matter for this sort of question... thanks in advance!