I don't suggest updating BIOS from within windows. Windows running adds another layer of crash possibility, and a bricked bios= a bricked board, although with ASUS, usually the bios chip is socketed and can be replaced.
I suggest:
Go to Asus Support website, type in MOBO name, find latest bios, download it to a FAT32 formatted USB stick with nothing else on it, plug that stick into a USB 2.0 port, reset the machine and enter bios (usually by spamming DELETE on ASUS boards) and find the Bios Flash option in bios. The PC may need to restart itself a couple of times after you flash. Whatever you do, don't turn it off or screw with it until it gets back into Windows. A botched bios flash is a terrible thing to do to a board.