TheScullster wrote:
Hi all

This weekend at about 12:30, I arrived home to find two messages on my
answer phone from the boss asking for help with his laptop.
So, incoming calls OK.
Using an old (unpowered) phone in an upstairs extension socket, so I could
be next to computer, I dialled his direct number.
The line was dead.
Next I went downstairs to try cordless phone, in different extension, dead
also.
So I unscrewed the customer side front plate on the master box to disconnect
all the extensions and plugged the unpowered phone in - nothing.
snip
Is there a reason for lost dial tone? All I could think of was an
off-the-hook phone, but we had received incoming calls while absent.

Unplugging the extensions indicates probably not.