Restore default registry key

Question

I associated "Unknown" files with notepad.exe, that is to say files with no or unknown extension.

HKEY_CLASSES_ROOT\Unknown

However I am not certain of the keys I changed to that effect. I would like to restore all Keys and Values under Unknown to their "default" state, if possible.

Answer 1

You can pull default registry settings from Windows 7 ISO without even reinstalling Windows. The following will create a Virtual Hard Disk to save the data you get from the ISO

diskpart
create vdisk file C:\wo.vhd maximum 10
attach vdisk
create partition primary
format
detach vdisk

Install VirtualBox. Create a new virtual machine. Make sure to choose "Use an existing virtual hard drive file". For the new virtual machine choose Settings Storage IDE and add the ISO file. Start the virtual machine. Once its started you can export a key (Shift + F10)

reg export hkcr\unknown C:\unknown.reg

Now power off the virtual machine and close VirtualBox Manager. Run the following to mount the VHD, then the REG file will be available on the host computer. Be careful not to run this too soon after closing VirtualBox. If you reattach before the VirtualBox process terminates the file will not be saved.

automount scrub
attach vdisk

Final result

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\unknown\shell]
@="openas"

Answer 2

I'm not sure what you're after, but this is a screen shot of my Unknown folder in my registry

Answer 3

Deleting the following keys should un-associate whatever default open application you've selected for unknown type files:

HKEY_CURRENT_USER\SOFTWARE\Classes\Unknown\shell\open
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Unknown\shell\open

They may not both exist, but that's ok. Leave the other shell verbs (probably at least openas and opendlg alone).