I am trying to update the ROM on my A81G. I have looked at lots of Youtube videos and tried multiple variations of starting the device with the power and Vol - keys simultaneously depressed, but it never goes into ROM update mode. It just boots up normally, although if I continue to hold the keys down for the first part of the boot process it will turn off the device. If I let it boot it boots normally. It never tries to load the new ROM. Any advice of how I can make this thing obey and get the new ROM installed?