The Windows registry keeps track of all hardware devices that have been installed on the machine.  By default, the Device Manager only displays the hardware devices that are currently connected to the machine.  Hardware that is not currently connected, such as a USB device, or a Firewire hard disk is not shown.  Over time, a lot of devices can be registered, particularly if you connect the same device to different USB ports.

By using an environment variable, you can have the Device Manager display all the hardware that have  been installed on the machine.  Set the “devmgr_show_nonpresent_devices" environment variable to “1” using the System Properties dialog.  Alternatively, just type set devmgr_show_nonpresent_devices=1 at a command prompt.

Then using Device Manager, make sure the "Show hidden devices" option is set on the view menu.  Normally when "Show hidden devices" is set, only non-PnP devices are shown.  With the environment variable set, Device Manager also shows disconnected hardware using a semi-transparent icon.  You can then uninstall the device and all the associated drivers.

An easy way to load Device Manager is to type devmgmt.msc at the Run dialog or command prompt.  A quick way to get to System Properties is to press Win+Break.

[This posting is originally from my blog at http://weblogs.asp.net/chuckop/.  I’m trying to move the more useful postings over to my current blog host.]