From LedHed's Wiki
Remove Hidden Devices from Device Manager
Some devices will not show up in Device Manager even when you select "Show Hidden Devices"
To display these devices (so that you remove them) do the following:
From a DOS Box run:
set devmgr_show_nonpresent_devices=1
Now launch the device manager:
devmgmt.msc
Then click "View" -> "Show Hidden Devices"
Now you should be able to see and remove lingering devices that are no longer physically attached to your Computer.