We dont have the serial number the bastard who sold us the device removed it.
Shoulda refused that item on the spot. In my books - wiped serial = stolen goods = I don't touch it.
The reset button is like the reset button on your PC. It reboots the device.
Have you tried reset, hold down the reset and unplug the power source from the device (*Not the wall) while keeping it held, plug back in with the reset depressed. With most enterprise routers I've encountered (Snapgear, Ramp, Sonicwall Soho & TZ, Watchguard) - this is the means to hard reset to factory defaults. This is also how I've fixed quite a few fucked enterprise firewalls myself.
( From what you described - sounds like you might not have tried this. This here should be the FASTEST fix you can find. I bet - you can fix up everything faster than you can ever find the answer to the requested how-do-you-disable-it from ssh/terminal question. )
You should have a clean from firmware configuration after that.