USB has decided to no longer work right...

Most (4/6) of my USB ports no longer work.
When I boot windows it says that there is a USB device connected when there isn't. This happens when a device (keyboard, mouse, gamepad) is plugged into one of the non-working ports.
In my Device Manager, whenever a device is plugged into a non-working port, it will flash a "USB Device" then disappear, then reappear, then disappear, repeating on and on...
I was wondering how I might go about fixing this.

When your computer boots, press F8 and choose to startup in Safe Mode and then delete the folder named System32.