Sierra won't install From my mac OS 10.8.5 I downloaded OS Sierra from app store. It said it was downloaded and the icon was in my apps folder. I clicked it, agreed, gave my password, but it wouldn't install.

Per advice from Mac Support, I dragged the download to trash, and did a new download (took 22 hours). However, that one will not install either. I tried restarts, holding keys down and everything suggested, but still nothing.
It's a mac mini 2013, OS 10.8.5. I gave the serial numbers to Mac Support over the phone and they said it should work.

Why will it not install?!
It is a 5 Gb file.

Find a place where you can download it in 1-2 hours (22 is not good).
Apple store can do it for you!
or at Starbuck coffee shop you can do it in about 2 hours :)

Also, Verify the downloaded file is correct.

Open a terminal window up (Applications -> Utilities -> Terminal) then type:
cd "/Applications/Install macOS Sierra.app/Contents/SharedSupport" with those double quotes.

then type in:

shasum InstallESD.dmg


and after a couple minutes it should return:
139ef35e4af0da8286b2a3af326cb114d774f606  InstallESD.dmg