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#11
I had a similar problem on an MSI Z87-G45 motherboard recently, and it turned out to be a progressively worsening problem with the BIOS chip itself. As long as you can access the BIOS, you'll be able to keep using that system. But if it's anything like mine was, eventually you'll get only error messages from the BIOS itself and it won't boot any more not even into BIOS/UEFI. I switched motherboards when I could only get A2 (SATA error) or 99 (USB error) codes from the system and nothing more than that. Sorry for your trouble.
HTH,
--Ed--
Thanks Ed. So.. best see if you can get some expert hardware advice... you can find some references to this report on the internet - nothing very definitive.
Just search for (e.g.)
EFI Shell Device mapping