Hello.I have too experienced the phenomenon where upon clicking on "play" for Dishonored, the Steam client will ask you-depending on whether UAC is on and it's settings,it WILL ask you if on default level at Windows 7- if you allow it to make changes to your computer's configuration.

The reason this happens is because the game needs PsysX Software version 9.11.1111 or higher to be properly installed, regardless of your actual graphics card chipset-AMD,NVIDIA-.On AMD based system configurations-with an AMD graphics card installed- unless you have manually downloaded and installed the latest publicly availlable version, you had the above version installed during initial set up thus you are never seeing the installation message prompt everytime you start the game.On NVIDIA based system configurations-with a NVIDIA graphics card installed-the latest official available version is the 9.12.06.04 which if you installed the latest WHQL driver version 306.97 is allready installed.The 9.11.1111 version setup will properly detect any higher version above it installed and will terminate it's own process accordingly,but it will try to reinstall itself upon the nexttime you will start your game.

Apparently this is something, Arcane Studios is aware of and they will need to address it in a future title update.Until then, our only option,and this is what I followed too of course is that you should click on "no" everytime the Steam client will ask you about making changes to your computer configuration whenever you start your game.

I hope this helps people with the above problem.