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It's my understanding that after downloading macOS High Sierra, you're now getting the question mark folder on your screen. I may be able to help with this. Check out this article: About the screens you see when your Mac starts up
Let me know if this helps.
Other screens you might see
You might see one of these screens appear during startup if you've changed your startup options, or if there's an issue starting up your Mac.
Folder with a question mark
If you see a folder with a question mark appear instead of the Apple logo, it means your Mac couldn't find a local or network-based startup disk. This can happen if the disk selected in the Startup Disk pane of System Preferences isn't available. Wait a few seconds to see if your Mac is able to locate the startup disk you specified.
If a question mark appears after you install a software update, select your startup disk again using macOS Recovery.
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