[DiapDealer]

The correct runtime comes with Sigil. It just doesn't try to install it if a minimum version of a compatible runtime is detected as being installed. Newer versions of Sigil also give the option to skip the checking/installation of the c++runtime altogether when installing. No one should really exercise that option if they don't know whether or not they already have a compatible runtime installed.

If renaming the Sigil.ini doesn't work (and no new Sigil.ini is created), then I'm out of ideas. I've never seen a situation where the default Sigil.ini would not be created.

You mentioned calibre, so I have to ask if you're launching Sigil completely separate from calibre, or if you're launching it via calibre's Open With feature/plugin.

Check the app logs in Windows' Event Viewer for any Sigil-related errors. Might be a clue there. You can also exempt the Sigil exe and directories from any malware scanners you may be using. We've had one report of back-up software flagging Sigil and not letting it launch.