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#720
There is no way installing Windows 10S can affect the bios. Something else is wrong.
What you could try is putting the hard drive in another pc, instead of its hard drive, installing correct windows 10 on that, and start it up, and at first screen when it asks for keyboard entry, press Ctrl+Shift+F3 which jumps you to audit mode, and a sysprep box should popup. Select oobe, and generalise, and shutdown and it will remove hardware drivers, then shutdown.
Then put drive back in other pc, and it will restart as if fresh from factory.