When trying to use Registry Editor and it's not working, including not opening, crashing, or the error message "Registry Editor has stopped working," here are some steps to try.
1: Registry Editor Not Working - System File Checker
Open File Explorer again and go to C:\Windows.old. Copy regedit.exe to the Windows folder.
If Regedit.exe isn't restored, or you don't have a Windows.old folder, you'll need to rerun System File Checker.
3: Registry Editor Not Working - Everything Else
There are other possibilities to consider. Try rebooting. Check to see if there are any pending Windows Updates. If you really get stuck or think you got infected, you could use System Restore or Reset This PC.
Finally, if you're in a hurry to make a registry change, you can use a third-party app. RegCool is one of the only freeware apps that is available as a portable app.