来自官方的说法：

　　SOLUTION: you need to reinstall PhysX drivers。

　　Uninstall current one, than install PhysX_10.05.12_9.10.0512_SystemSoftware package manually,

　　from \Steam\steamapps\common\mafia ii – public demo\3rd

　　1. run GPU-Z, no Physx

　　2. go to(c:\Program Files (x86)\Steam\SteamApps\common\mafia ii – public demo\3rd\)

　　3. run PhysX_10.05.12_9.10.0512_SystemSoftware.msi, uninstall physx

　　4.run again PhysX_10.05.12_9.10.0512_SystemSoftware.msi install physx

　　5. run GPU-Z, Physx oh YES

　　6. run Mafia 2

　　我的还没下玩，有安装过的可以试一下。