Unable to connect to bt_test@startup_domain

Hi,

Following a power cut at the weekend I have been unable to connect to
my Demon broadband account and am getting nowhere at all with Demon
support who only seem able to read from a script these days. Absolutely
the only thing which happened to the router between it working and not
working was a power cycle (no settings were changed).

The situation is that the router synchronises with the exchange (ADSL
status = SHOWTIME and the SNR is good), but then it appears that it
can't log on (PPP status = disconnected). If I try a manual PPP connect
it says "connecting" for a period of time (perhaps 10-20 seconds), then
says "ERROR" and goes back to disconnected.

The router's status information and diagnostics are not brilliantly
clear, however it appears that the ATM loopback tests are ok, but
password authentication is failing (or possibly it's a general failure
of PPP). I get exactly the same error whether I log on with my demon
account details or "bt_test@startup_domain".

I've checked all the router settings (VPI=0, VCI=38, PPPoA, etc.) and
I've even tried a "reset to factory defaults", however it still sticks
at the same point.

Can anyone explain to me what it means if I have ADSL synchronisation
but can't log onto bt_test@startup_domain. Could a failure of equipment
at the exchange cause this or does it mean my router is definitely
faulty?

I'm going to borrow a different router this evening, but assuming it
fails at exactly the same point, are they any magical phrases I can
speak that will cause the support droid to jump to the right bit of his
script to progress this further?

If its of relevance, the router is an Origo ASR8400 which has been very
reliable over the 2 years I have had it.

Thanks,
Martin.