Aliases/Diag_tables suddenly empty and firewall not working

[brtech]

Came in to work to find no pcs had internet access.

Checked logs,  no obvious errors.  Checked alias status page (Diag_tables.php) and it says "no entries exist in this table".

Rebooting has not resolved it,  nor has restoring a backup from when the router was working.
As far as we know nothing else has been changed (hardware,  switches etc).

Does anybody have any ideas of what i need to look at to resolve this?  I'm stumped at this point.

Please excuse typos,  using phone to post this. Thanks