How do I DISassociate a file type in Windows 10?

I really did it this time.  I was working on a .dat file.  I know it's an unknown application; but I was preoccupied with something different.  It was brought up and I accidently set it in a program.  How do I disassociate the .dat file to be an unknown application? 

I searched in the control panel and found indexing options.  I opened it up and clicked the advanced button.  In the advanced options window, there is a troubleshooting section that deletes and rebuilds the index.  Should I use that?  Thank you for your help.


I followed these steps up to export, changing .dat to .tmp.  I didn't know what to do after that.  I guess I really didn’t do anything.  This is what I have.


WinKey + X - Command Prompt (Admin) - type in -> Regedit


In left pane scroll down to .dat and click on it.

Right Click on it and EXPORT so you can recover if there is an error.

Still in the left panel under .dat delete the one or two sub-keys but not the
.dat itself or the info in the right panel when the .dat is highlighted.

So now when .dat is highlighted there is no sub-keys and in the right panel is 

(Default)   value not set        <-- if you click on it data field is empty
NoOpen                               <-- if you click on it data field is empty 

Close Regedit and Reboot the computer.

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Question Info

Last updated September 22, 2020 Views 42,242 Applies to: