Windows 7 lacks native USB 3 support. Wouldn't be surprised to find that lack of support means problems for USB 3 docks at the login screen. On a pure USB 3 system, you have to embed drivers on the install disc/usb stick to have a working keyboard and mouse during setup.

http://codeabitwiser.com/2014/03/how-to-install-windows-7-with-only-usb-3-0-ports/

Windows 8, and Windows Server 2012 are the first versions to have native USB 3 support.