You need to flash in pure dos with the /forceit switch. Use a bootable usb thumb drive, place the bios update file at the root of the drive, then boot from the thumb. At the prompt, type in the name of the bios update .exe file followed by "/forceit" without the quotes, hit Enter. Note, there is a space between the e on exe and the /.
Keep the mains connected during this process and if you have a UPS, then stay connected to it.