KF2 Not Responding on Launch: Vista Compatibility Fix

During the 2015 early access period some players found that starting Killing Floor 2 produced a frozen, windowed "KF2 DX11 64-bit (Not Responding)" window and tied up the whole operating system until a hard reboot. Most troubleshooting advice at the time focused on Nvidia cards, so one player shared the sequence that worked on Windows 7 Home Premium 64-bit with an AMD Radeon GPU. After applying it, offline solo mode ran many times without trouble.

The five steps

1. Delete the local files of Killing Floor 2 from the Steam library (uninstall the game).
2. With Steam fully closed, delete ClientRegistry.blob from the Steam folder and reboot the PC.
3. Re-download Killing Floor 2. When it finishes, close Steam again and delete the PhysX folder in steamapps\common\killingfloor2\_CommonRedist.
4. Open the properties of KFGame.exe, go to the Compatibility tab and tick both "Run the program in compatibility mode for: Windows Vista" and "Run this program as an administrator".
5. Reboot, then start the game.

Extra tip from the comments

If it still fails, add -dx10 as a launch option in the game's Steam properties. This forces the DirectX 10 renderer, which also helps in other launch problems (see Instant crash fixes).

The author credited a forum user for suggesting most of these fixes in the official Steam discussion thread.