Same thing happened to me on my new PC. It drove me nuts until I finally figured out it was the dual core processor causing the issue. So like the guy above me said, just set your processor affinity. You have to do this each time you start the game. If you don't want to have to do this each time then download a program called imagecfg. It will allow you to associate a particular program file with a particular CPU permanently. It works great with RomeTW.exe but I've had issues with it working with other programs.