When I leave my system running too long, say running a long download for a game, I come back and the screen goes black and it says "No bootable device" but it clearly was booted to begin with and I tried a fresh install but that continually fails even with Windows 10 bootable media on a usb drive
Try making another source for the installation media. I've ran into corrupted ones before. If that fails then you [strike]defiantly[/strike] definitely know something is wrong with the hard drive. If you have another computer you could pull the hard drive and test it to see if it has gone bad for sure.