I have this alarm but haven't used it in years. Now it has error code of FC that goes off everymorning at 5 am! Like I said I am not using it and it hasn't been monitored or had a phone connection in years. But I think some recent power outtages started this. So how can I just disconnect it all? Thanks!

Been a while on the Vistas, but believe it may be Failure to Communicate.
Are you able to do any Programming? You can disable communications.

Also on the master panel check for a fuse. If it has one then by removing it you won't have power to the unit.

I just realized you want to disconnect it all.
If so, remove the Transformer and disconnect the Battery can't hurt.