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。