My USB 3.0 was so munted with drives dropping in an out on an HP8460p (with Windows 7 older than the PC and never rebuilt). It occurred after plugging in a suspect broken drive some months ago. All the drives would work as USB 2.0. I had a go at finding all the registry keys but failed. I was beginning to think it was hardware.

I then discovered drivecleanup and devicecleanup ( see http://www.uwe-sieber.de/drivetools_e.html) on a message here http://www.techspot.com/community/to...rivers.145884/

Problem solved.

I used both tools and could not believe how many obsolete hardware devices were there.