I believe you have to see the screen (run through menu options) to select factory reset.
Did you back up your waypoints/trails/etc before you inserted the update SD card? On Humminbird PC?
If yes, I'd power down the unit, go to the store and purchase a new SD card, make a new update SD card and try to load it.
SD cards can get corrupted, so to be safe, I'd either throw away the old one, or do a complete format of it to be used later.
The Longhorns are back