I can't update the BIOS (28-->33) on my NUC6i5SYH. I've tried the .bio via F7 and the visual bios, as well as the dos disk method. After starting the update the unit powers down, the yellow light flashes and nothing happens for hours. I can restart the nuc by holding power down. The first boot gives me three beeps with blue light. After holding power again it boots up, with bios 28. Any ideas?