Help needed: Humminbird Matrix 10 Fishfinder

Hi Everyone,

I need some help with my fishfinder, I upgraded the firmware with version
2.480 (got it from Humminbird web site) and it is now not able to start.

When I press the power buttom, the startup screen show for about 2 second
and then it goes into the normal mode and then it will power off
automatically.

With the menu button, I can goes into normal, simulation, system status and
pc connection and that it.

I'm thinking there might be some key sequence will restore the system to
default or if someone can provide me with a older version of the firmware.

Thanks alot.
HH