If you decide to update your BIOS it is absolutely ESSENTIAL that you select the correct BIOS update for your motherboard as if you select the wrong one then your PC won't boot up at all.
Also if you were to suffer a mains power cut or PC crash DURING the update this too would stop your PC booting up. Having said this BIOS updates are normally quite small so the procedure shouldn't take more than a minute or two and you would be VERY unlucky if something happened during this short space of time!
I personally have a Gigabyte motherboard with the Dual BIOS feature so even if something DID happen to the main BIOS there is a backup to boot from and which I can use to copy the working data onto the corrupted BIOS chip. CW