In Control Panel>Folder Options>File Types find both .txt (assuming that works well) and .ini. Compare the details of their open options and correct the error.
It might work also to choose the the right click "open with ..."
for an ini-file, and reset it to, say, Wordpad, then again to Notepad. Windows will redo all settings, and that should correct the problem also.
When I double click a .ini file in windows explorer, notepad opens with the following message:
"The filename, directory name, or volume label syntax is incorrect." and a blank file appears.
Any suggestions on what's going wrong?