Issue

Device Manager displays only non-Plug and Play devices, drivers, and printers when you click Show hidden devices on the View menu. Devices that you install that are not connected to the computer (such as a Universal Serial Bus [USB] device or “ghosted” devices) are not displayed in Device Manager, even when you click Show hidden devices.

Workaround

1. Click Start, click Run, and type:

   cmd

2. Click Ok

3. At the command prompt, type the following command and then press ENTER:

   `set devmgr_show_nonpresent_devices=1`
   

4. Type the following command at the command prompt and then press ENTER:

   `start devmgmt.msc`
   

5. Troubleshoot the devices and drivers in Device Manager.

   Click Show hidden devices on the View menu in Device Managers before you can see devices that are not connected to the computer.

   Note that when you close the command prompt window, Window clears the devmgr_show_nonpresent_devices=1 variable that you set in step 2 and prevents ghosted devices from being displayed when you click Show hidden devices.

If you are a developer or power user and you want to be able to view devices that are not connected to your computer, set this environment variable globally:

1. Right-click My Computer
2. Click Properties
3. Click the Advanced tab
4. Click on the Environment Variables tab
5. Set the variables in the System Variables box

Use this method only for troubleshooting or development purposes, or to prevent users from accidentally uninstalling a required device that is not connected to the computer (such as a USB device or docking station that is not connected to a laptop computer).

Reference

http://support.microsoft.com/kb/315539