No PPPoA connection for 2 days

[#1]

I've had no PPPoA connection - and hence no Internet connection - for the past 48 hours.
The router is otherwise working OK. In particular the ADSL link trains with normal upstream and downstream connection speeds.
My phone is OK.
Repeated power cycles of the router make no difference.

[#2]

Are you using a Plusnet router & how old is it?

[#3]

No, I've been using a Netgear DG834Gv5 for the past 4 years or so.

[#4]

I'm guessing you have already tried ensuring the username and password is right and tried apply/connect again?
If you have then there are two likely scenarios;
1- Router has died (quite possible with it being 4yr old)
2- A service outage in your area,  these don't tend to last 2+ days though very often.

[#5]

My router was working OK until I powered it off on Monday night. When I powered it on on Tuesday morning there was no PPPoA connection. I hadn't changed any settings.
Apart from no PPPoA, there is no obvious problem with the router: WLAN is OK, statistics are OK.
I'll login to my router via telnet and see if I can find relevant error logs.
Alas I don't have another ADSL2+ router to try.

[#6]

Did you unplug it on Monday?  check the pins on the plug/socket  in case one got bent.
Have you tried in the test socket if you have one?
Tried a different filter/ ethernet cable.
Please post the logs./stats

[#7]

It's worth trying to just re enter your details and apply/connect again and if that doesn't do the job then do as cedlor mentioned and try getting it connected again.
If that doesn't work and you are getting the sync/dsl connection side of things then it is almost definitely the router.
Worth checking for service outages also before going any further as if there is one, your answer is right there and you can save yourself alot of fiddling;
http://btbusiness.custhelp.com/app/service_status/

[#8]

Also worth checking if you could have been affected by maintenance work and something might have subsequently gone wrong -
http://usertools.plus.net/status/archive/1439807535.htm

[#9]

A more useful test is to try logging on with the username [tt]bt_test@startup_domain[/tt] - the password can be anything or just blank.
If that gets you a working PPP session then you won't get internet access, but proves your line is OK.
If you don't get a connection, you'll need to raise a fault with PlusNet.
If you do get a connection, the next step is to disconnect, and try connecting with [tt]bt_test_user@plusdsl.net[/tt] (same password rule).
As above, if it connects you won't get internet, but it proves your line is OK and you are connected to the PlusNet domain.
If that doesn't connect you'll need to report a fault to PlusNet. If either of the above connect, then put your own username and password back in, taking care of the case and making sure that CAPS LOCK and NUM LOCK keys aren't causing you to type incorrect characters in your password.
Last resort - if you don't have another router to try, see if you can borrow one from a friend/relative/neighbour, so long as they know it works and it isn't locked down (so Sky and IIRC TalkTalk routers won't work).
Lastly, if it turns out to be the router, and you replace yours with something newer, don't switch it off. Ever.

[#10]

I found the problem via telnet into the router. Running syslogd showed that the PPP daemon could not authenticate via CHAP (Challenge-Handshake Authentication Protocol).
I had indeed changed my Plusnet password and forgot to update the router.
Oh dear.
Thank you all for the suggestions.