I suspect the OP would like more help!
Briefly, start by checking the external mains supply is OK. Beyond that the panel will need testing. If opening the panel, turn off mains. If known, enter engineers code, open panel, (without engineers codes, silence bells by entering owners code) and check mains supply, fuses and battery.
Hopefully problem found. Close panel, restore mains and reset.
The engineers manual is available on line and careful reading, understanding and circuit testing will enable you to work through your problem, if it is not a failed battery and fuse.