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How I Fixed a USB "Unknown Device" Error

My son's printer stopped working on his Gateway laptop. When plugging into any USB port, the generic "Unknown Device" error balloon displayed in the tray area. I tried other cables, printers and even USB Drives and all got the same error. The printer was immediately recognized in a desktop, even though there were no drivers installed for it.

I had tried uninstalling the Unknown Devices from the Device Manager and even the USB Hubs and Host Controllers then forcing a "scan for hardware devices" to get them re-installed. Plugging the printer back in still resulted in the Unknown Device.

I eventually tried this suggestion from Experts-Exchange.com which fixed the problem. It lets you see other hidden Unknown Devices and Other Devices in the Device Manager. Uninstalling everything USB related and then plugging in the printer (with no reboot) got the printer recognized immediately.

STEP #1: Create a system environment variable that will allow you to see nonpresent devices in the device manager.

START->SETTINGS->CONTROL PANEL->SYSTEM icon->ADVANCED tab->ENVIRONMENT VARIABLES button
Click NEW on the bottom of the SYSTEM VARIABLES frame.
Enter the following:
Variable name: devmgr_show_nonpresent_devices
Variable value: 1
Click OK and close the SYSTEM/CONTROL PANEL windows.
(It is very important to spell this exactly as it appears.  If you mispell it, you'll know it because you won't see a "ghosted out" Unknown Device later on.)

STEP #2: Open the DEVICE MANAGER, enable VIEWING HIDDEN DEVICES, and locate the UNKNOWN DEVICE

START->SETTINGS->CONTROL PANEL->ADMINISTRATIVE TOOLS icon->COMPUTER MANAGEMENT icon->DEVICE MANAGER folder
First, we want to enable viewing hidden devices.  The environment variable gives this a second functionality as well, to see both hidden and disconnected devices.  From the menu, select VIEW->SHOW HIDDEN DEVICES
After that, find the device tree called "Universal Serial Bus Controllers" (it should be the last thing in the list).
Expand this tree, and you should see the UNKNOWN DEVICE somewhere in there.

STEP #3: Unplug the USB device

Now, unplug the USB device, and the UNKNOWN DEVICE should sort of "ghost" out a bit.  If it disappears completely, either "Show Hidden Devices" isn't checked, or the environment variable was spelled wrong.  Close everything, check the environment variable, and try again.

STEP #4: Uninstall the "ghosted" UNKNOWN DEVICE

Right click on the "ghosted" UNKNOWN DEVICE and select Uninstall.  Do not accidentily uninstall anything else in the tree!  The UNKNOWN DEVICE should now disappear.  If there are any other UNKNOWN DEVICES that are also ghosted out, uninstall those as well.

STEP #5: Plug the USB device back in

When you plug it back it, the USB device should now be detected properly.  If not, .....  then well... I tried :)

Good Luck!

Print | posted on Saturday, August 11, 2007 12:00 AM | Filed Under [ Personal ]

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