if they're not working at all, try installing the newest usb drivers. If it's an intel system, download the inf support package from intel.com and if amd download their chipset thing. if any other, it's unlikely it'll need fixing.
If all else fails, enter the registry and delete all devices under HKLM/system/currentcontrolset/enum/usb
You need to set access to full control first, and meddling with the registry is risky indeed. Don't do so without good reason.
I would probably expoert the enum/usb tree before playing with that.