Recently I had a client that could not install any new hardware drivers on her laptop.  Setupapi.dll would crash during the installation process.  She had over 200 pieces of malware on her pc so I can only assume one of them modified setupapi.dll.

I took a chance and copied a setupapi.dll from another pc (a clean pc that had the same version of the dll) and she was able to install all her hardware drivers.  I love when simple things work.