Try uninstalling with DDU (Display Driver Uninstaller) and then installing the latest drivers. If that doesn't work, DDU again and install the old drivers. If that still doesn't work, then odds are you've got something else that is conflicting with your game. It could be anything that you've installed since then, a new program, a Windows update, a piece of malware or even a virus. So make sure to run a virus scan with a decent virus scanner. If none of the above helps, try closing down programs one at a time. Your web browser for instance might be using your GPU in the background, also try closing the apps in the System Tray.
