For future reference, 9 times out of 10, if it comes up as wrong boot device, (and the bios is set to the correct order) it's the hard drive failing or failed.
What you can do in these situations, is yank the drive(easy if it's a single panel) slave it to your test machine, and run drive diagnostics.
I do that all the time with clients.
If I have to strip it, I tell them I can't do it whilst they wait.
It usually fails, or gut instinct says its failing I go into upsell mode and get them onto a ssd. And say they can have it back following day.
If it has windows 8 or 10 already installed on it, it will activate automatically.