How can I change dat file extension back to unknown file?

[masterx]

Hi,
I don't know how to restore file type association in Windows to the default state with no associated program.

In Control Panel -> All Control Panel Items -> Default Programs -> Set Associations: When Windows not know which app should open a dat file type, it assigns a blank default icon to this file.
In my case, I associated dat file with wrong program by mistake and forgot to uncheck the box Always use the selected program to open this kind of file in open unknown file dialog. How do I delete/restore it?

[Malric]

You can generally deselect certain filetypes in start -> default programs -> set your default programs. Just select the program from the list and click on the choose defaults for this program which will show you list of types associated with it. Decheck the box and save it.

[ooilverhawk]

it assigns a blank default icon to this file.