Device Manager displays information about the hardware devices installed on your computer. When it comes to troubleshooting, it can be an invaluable tool. However, you may not have noticed that Device Manager does not actually list all the hardware.

Two types of devices are hidden in Device Manager: non-plug and play devices and ghosted devices (nonpresent). You can easily force Device Manager to display non-plug and play devices. Right click My Computer and click Properties. From the Hardware tab, click Device Manager. Select Show Hidden Devices from the View menu.

Forcing Device Manager to show ghosted devices requires a little more work. Right click My Computer and click Properties. From the Advanced tab, click Environment Variables. Under System Variables, click the New button. Type devmgr_show_nonpresent_devices for the Variable Name. Under Variable Value, type “1″ and click OK. Click OK twice more to apply your changes and exit the System Properties dialog box. Now open Device Manager again and from the View menu, click Show Hidden Devices.