Pull the cards, remove the metal stand-off, set the battery switch to off and switch 4 off. Make sure to disconnect the power cord so the batteries drain. plug it all in again after a minute or so and it should be defaulted to a base 308 cabinet. Make sure to upgrade to the latest software.

You may want to upgrade to the latest software before defaulting it and removing the VM and expansion card. The voicemails act really weird if they're plugged into a system with a different software rev. I had that happen to me today.