[alecE]

Running Win 7 Home Premium 64-bit. Uninstalled 0.9.5, began installation of 0.9.7. All went well, then got a 100% progress bar plus the message saying "Checking for VS 2015 Runtime...", followed by a second window saying "MS Visual C++ 2015 Redistributable (x64) - 14.0.24210", also with a 100% progress bar.

At this point there was no evidence of any activity; decided the install was going nowhere after two and a half hours and hit Cancel. Whereupon the install appeared to finish normally. Trying to run Sigil failed because a dll was missing. Reinstallation took approx 10 seconds, running Sigil failed again with the same message.

Both times, Sigil was started from its icon, not from within Calibre.

Uninstalled Sigil 0.9.7 and re-installed 0.9.5, which appears to be running perfectly.

Problem with Sigil or problem with Microsoft?

EDIT
Definitely one of those days where the thought of a life without Microsoft seems attractive.

Following info in other posts, I tried to install Visual C++ redistributable 2015 after downloading it from MS. First attempt failed 'cos the previous attempt via Sigil was still in evidence. Uninstalled both versions (14.0.24210 & 14.0.24215) and tried again. The installation hung. Uninstalled the failed install and decided I can live without it pro tem.