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The Device Manager lists the devices that are installed on the machine. By default, certain devices are not shown in the list. These "hidden" devices include devices that have the devnode status bit DN_NO_SHOW_IN_DM set and devices that are part of a setup class that is marked as a NoDisplayClass in the registry (for example, printers and non-PnP drivers).
To include hidden devices in the Device Manager display, click View and select Show Hidden Devices.
Another category of devices, not shown in the Device Manager by default, includes devices that have been physically removed from the machine but whose registry entries have not been deleted. These devices can be considered "nonpresent" devices. Users should never need to view such devices because a nonpresent device should not need their attention and should not cause any problems. If a user needs to view your device when it is not present, there is likely a problem with your driver design.
During testing, however, you might need to view such devices. To view nonpresent devices, open a Command Prompt window and type the following command:
set DEVMGR_SHOW_NONPRESENT_DEVICES=1
(You can also set this value in a permanent environment value using the Advanced tab of the system property sheet.) After you set this value, run the Device Manager and select Show Hidden Devices.