Game ran perfect last night; now terrible.

[Wheem]

As the title says, my game ran perfectly fine when I was playing last night.

Now, however, I have really awful video lag. It stutters pretty bad when I scroll across the map (even if I start a new game and can hardly see any of the map), and the "swirling circle" thing under the selected unit is also visibly stuttering. All graphical settings seem to be the same that they've been set on for a long while now. Still, I changed the settings to be extremely minimal, but the stuttering persisted.

Also, all of my map settings seem to have been reset. In the past, when I went to start a new game, most of my settings remained the same as they were the previous game I'd played; while the only things that were reset were my Civilization, number of continents, and island size (with Hemispheres map selected). Now, it keeps resetting my difficulty (from Prince to Chieftan), my map to Fractal, world size, victory conditions, etc...which is very annoying.

I have absolutely no idea what would cause this to happen, since I've not changed anything at all on my machine; hardware or software. Civ4 seems to be the only thing affected...

[Wheem]

Well, I still have no idea what caused the issue, but loading up the original game (no expansions) with original disc had it running fine (didn't try Warlords). Going back to BtS brought back the terrible video lag. Uninstalling and reinstalling BtS fixed it though.