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Fix damaged or absent external USB drives

When a USB drive stops working often times it's because the Registry key is damaged or has gone missing.

Like so many in this industry, I've come to rely on external USB-based storage devices: I have two hard drives in external cages, a USB flash drive, a music player that also works as a USB drive, and so on.

If any of these stop working, users and admins alike tend to blame the USB device, the USB controller or the PC in general. What's really frustrating is when a USB drive stops working on one computer but works fine in another. In this case, what specifically has gone wrong?

Why USB drives may not work
In the past, I've discussed how something similar can happen to CD/DVD drives if their Class entry—the Registry key that describes installations of that device type—goes missing or is damaged. Sometimes a third-party application might do this by attempting to install a filter driver for that USB device type; you see this sometimes with CD/DVD recording applications.

Fixing external USB drives
The same sort of damage, or interference, can also happen with external USB drives. The solution is to delete the damaged or malformed keys and allow the devices to be redetected normally. Here are the steps to follow:

  1. Open the Registry on the offending computer and navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E980-E325-11CE-BFC1-08002BE10318}.

  2. Delete any values with the name UpperFilters or LowerFilters within this key.

  3. Navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E967-E325-11CE-BFC1-08002BE10318}. (This is within the same general area of the Registry, but note the slightly different CLSID.)

  4. Also delete any values with the name UpperFilters or LowerFilters within this key.

  5. Reboot the computer.

Note: When you do this, any third-party applications (like CD/DVD recording programs) that added or changed UpperFilters or LowerFilters settings will no longer work correctly and may need to be reinstalled.

The second CLSID number (the one starting with 4D36E967) typically has an UpperFilters entry of PartMgr (a REG_MULTI_SZ value); this is the standard CLSID for disk drives. Many disk management products, such as Acronis TrueImage or Norton Ghost, may attach a filter here.

If you have installed more than one such product and they are conflicting, it may be possible to get them to work in harmony by reordering the names of the filter drivers. This can be done by simply editing the UpperFilters value and changing the order in which the drivers are enumerated. Note: This may involve some trial and error if you have multiple products installed that do this, some of which may not be designed to work with each other at all.

About the author:
Serdar Yegulalp is editor of the Windows Power Users Newsletter, which is devoted to hints, tips, tricks, news and goodies for Windows NT, Windows 2000 and Windows XP users and administrators. He has more than 10 years of Windows experience under his belt, and contributes regularly to and


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