Performance issues

Hello, I was wondering if anyone's experienced this problem and knows a solution for it. I have previously played the game on this PC, but with a different graphics card, and hadn't opened it in a while.

I tried playing today and with a new scenario, without any buildings or people other than the initial villagers, the game is stuttering and running with a lot of slowdown. I attempted changing the settings to the lowest ones but it's not doing anything, changing the resolution likewise does nothing. I've also tried repairing the game files in case something was broken but it all seems to be fine.

Processor is an Intel i5 750, 8GB RAM, using Windows 7 64 and the graphics card, the only bit I've changed since I last played, is an Nvidia GeForce GTX 570. Drivers are up to date and there's plenty of space left in my hard drive.

Any ideas as to what might be causing the slowdown?

[Rob .]

Reinstall the game? I don't see how there could be any problems with your hardware