I downloaded the High Sierra upgrade a few weeks ago and have tried to launch it now and then since, but it does nothing. Not even report an error.
The High Sierra icon with apparent stalled download indicator in my Applications folder
It does seem to start. I'm pretty sure I can see it when I run top in a terminal.
My machine is officially compatible. It's a mid-2013 11" MacBook Air.
It doesn't have an SSD, just a USB 3 external hard drive. But this didn't stop the last few OS upgrades from working.
I can't seem to find this specific problem mentioned anywhere on the net when I Google for it.
Is this actually a known problem with a solution?
Update
I thought I should try to run it from the terminal and see if it outputs an error there. But it is not a regular executable file. It is some kind of magical directory in fact that is associated with the App Store. So I don't know of a way to launch it from the terminal. Doubleclicking on it does something in the background using the App Store, since the App Store does not open or tell me anything.
Best Answer
Depending on when you downloaded the installer precisely, this answer may provide a clearer reason for the issue.
I have noticed that their have been one or two system updates for macOS High Sierra in the past weeks. The fact that you are encountering this issue is most likely due to the fact that your version is older than the currently available and up-to-date one in the Mac App Store today.
Please try downloading the latest version.
Then let me know how you get on with the install. This would be the only logical reason for it not working on a supported / compatible system.