daqui:
Eu aprendi isso:
Found it in the Registry. Only proceed if you are insanely frustrated with this issue.
Look at the value in the following key in the registry. HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts.jar\UserChoice
Does it look something like Windows\explorer.exe? Not good.
Delete the following key in the registry. HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts.jar\UserChoice
Now, you can go to an Explorer window and choose a new default program for .jar files.
Apliquei este conselho à extensão .txt e funcionou.
Infelizmente, a opção Novo arquivo de texto no menu de contexto do Explorer foi distorcida. Consegui restaurar isso a partir das seguintes palavras sábias (de link ):
you can re-create [a missing context menu item for New Text Document] by copying and pasting the following as text file into Notepad or Notepad++ and saving it as fix-new-text-document.reg. Last, double click on the file to import it into the registry. Windows will likely ask you to confirm that you really want to do it.
Windows Registry Editor Version 5.00 [HKEY_CLASSES_ROOT\.txt] "PerceivedType"="text" @="txtfile" "Content Type"="text/plain"