One of the reasons that Bios updates should never be done in Windows.
Bios updates should only be done if that update directly addresses the particular problem (s) you are experiencing.
Most likely your Bios chip is trash. If the Bios chip is removable, it can be replaced pretty easily. If it' soldered to the Mobo it needs to be done by a professional and that might end up being more than a replacement.
I found a BIOS chip for your model here: https://www.ebay.com/itm/BIOS-CHIP-ASUS-X751LD-X751LA-X751LJ-X751LX-X751MA-notebook-/381433345951
Did you try to reset your CMOS jumper settings in Mobo?