Viewing Hidden Devices
Device Manager lists the devices that are installed in the computer. By default, certain devices are not shown in the list. These hidden devices include devices that have the device node (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 Device Manager display, click View and select Show Hidden Devices.
Another category of hidden devices, not shown in Device Manager by default, includes devices that were physically removed from the computer but whose registry entries were not deleted. These devices are considered nonpresent devices. Users should never have to view such devices because a nonpresent device should not have their attention and should not cause any problems. If a user has to view your device when it is not present, there is likely a problem with your driver design.
However, during testing, a developer might have to view such devices. To view nonpresent devices, you must set the environment variable DEVMGR_SHOW_NONPRESENT_DEVICES to 1 before you open Device Manager, then open Device Manager and select Show Hidden Devices.
To permanently set the user environment variable DEVMGR_SHOW_NONPRESENT_DEVICES to 1, use the Advanced tab of the system property sheet. After you set this environment variable, run Device Manager and select Show Hidden Devices.
For information about how to set user environment variables, see "Setting environment variables" in the Help and Support Center.
For more information about hidden devices, see Hiding Devices from Device Manager.