I had that happen. If the file was corrupted on the last closing, mach may not be able to read it. Then it does just what you describe. A window flashes momentarily, the path and file name appear in the ‘File’ window but nothing else.
You might try opening the file in notepad and see if there is anything obvious. If not, copy the entire file and paste in another open notepad. In my case the new copy saved OK and the file then opened in mach.
al