Welcome to the forum. Sorry to hear you are having some issues. Did you restore the defaults before inserting the SD card?
Download a fresh copy of the update for your unit from Humminbird on to the SD card. Try to power up with the SD card in the unit and see if will try to do the update. If that doesn't work, turn it on and stick the SD card in and see if it will try that way.
If all else fails, you can get the PC Connect cable and restore thru the bootstrap mode. Let me know on the first ones and then we will get into how to do the bootstrap.