Go to device manager, find all USB devices (including 'hubs), right-click, uninstall. Unplug everything USB from computer, restart (via power button, since mouse/kb won't work).
You should get the "installing driver" balloon on bottom-right when Windows loads. Plug devices in one by one, making sure they all connect and register successfully.
If that still doesn't work, do the above again, but at the shutdown part do this: pull the power plug, clear CMOS (small battery, google it), press power button to clear residual energy, then boot it up and continue.