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Imagine that you have a situation: you’ve been installing and uninstalling some programs for a week or so, was switching your computer on and off, doing some other stuff but then you need to read a DVD and the computer does not recognise it. And I mean not just doesn’t recognise a DVD disk but doesn’t recognise your CD/DVD reader or writer i.e. it switches on, spins ok, the indicator is on but there is no activity on the pc - no popup windows, nothing. When you go to the Windows Explorer, it says “please insert the disk” when the disk is already inserted and so on. What do you do?

My first reaction would be to reinstall the DVD reader/writer drivers or to open the computer case and check all the wires because I could see that on its own the DVD device works fine, it just cannot be accessed by the computer. And at the end of the day maybe I would get irritated and try to repair Windows, which would fix the problem eventually…

But as I’ve learned recently (see barugon.wordpress.com/2008/08/01/windows-cannot-load-the-device-driver-for-this-hardware-the-driver-may-be-corrupted-or-missing-code-39) there are easier ways of fixing the unaccessible DVD or CD writer. The problem described above is usually caused by the newly installed software like Sony drivers or Sun drivers or any other that mess with filters in Windows Registry. What they do is they add custom - not recognised by Windows - LowerFilters and UpperFilters entries to the Registry thus preventing access to the CD or DVD reader or writer. A special CD/DVD disk control class that is affected is {4D36E965-E325-11CE-BFC1-08002BE10318} and the solution is to delete all the incorrect LowerFilters and UpperFilters entries for the above class.

In this case the newly installed devices or drivers may stop working but it’s not difficult to reinstall them later because the access to CD or DVD drive is one of the important functions in the computer. If after the reinstallation CD/DVD becomes inaccessible again, the newly installed software should be uninstalled completely and the manufacturer of this software contacted. In general I think that people and companies should not make the programs that prevent other programs on the computer from working or computer components from functioning correctly.

How to figure out which filters to delete and which filters to leave as they are? For that, a special Microsoft Utility DevCon (download it here: support.microsoft.com/kb/311272) can be run with the following parameters:

devcon stack gencdrom

It’s a command prompt utility and can only be run from command prompt. It will show which LowerFilters and UpperFilters exist in the registry and associated with the active CD/DVD drive. All that are dodgy and not easily recognisable i.e. not ‘redbook’ or ‘imapi’ can be removed. Simply delete their entries them from the registry, reboot the computer and the job is done. Before you do that, you may go on the Internet, check the filter entries out there and make your own mind out on whether to delete them or not.

The other way to figure out what filters are installed for the CD or DVD reader/writer is to install the DevFilter Utility, which can be found here: www.bustrace.com/products/devfilter.htm. I did not install it because I didn’t need to but from the print screen on the website it looks fine and shows exactly what’s required.

If you’re a cautions person, you can delete filters one by one starting with the dodgiest ones, reboot the pc every time and see what happens. In my case I have had a couple of unidentifiable LowerFilters and UpperFilters entries, which I’ve deleted. Then after I’ve rebooted the computer, Windows for some reason has re-scanned my Windows user settings but it recognised DVD writer again. The user settings scan and partial reset was weird but everything worked fine.

There are multiple Microsoft articles and workarounds regarding the missing CD or DVD drives but all of them are related to the manual removal of LowerFilters and UpperFilters entries from Windows Registry. So instead of wasting time and following each one step-by-step, it’s in my opinion easier simply to get the hands dirty by running DevCon or DevFilter, get inside the registry and remove at once everyting that is suspicious or not recognisable.