Well, I just bought a webcam and decided it would be better on another computer, so I moved it. But when I uninstalled the software for my webcam on the first computer, it deleted some sort of driver that the other devices require to operate. And when I installed the software again it apparently put the driver back, causing the other devices to work again. I did this twice to confirm.
My advice is this: If you uninstalled some USB device when your problem started, install it again. (If you ever had any USB device on your computer and you don't have it on that computer anymore then try installing it on that computer again, I think it's worth a try.)
Another thing you can do is to go in to the Device Manager and look for "USB 2.0 Root Hub" Or something named like that, and open the properties for it, click on the "Driver" tab, click on "Update Driver", click "Next", select "Display a list of known drivers", click on "Next", select "Show all hardware of this device class", and start browsing around trying to install different drivers.
I really feel for you all, I know what you're going through because it happened to me. I will do my BEST to help.
P.S.
I'm sorry if it's hard to understand what I'm talking about but I have a busy week, therefor I have to be quick when I write this stuff.