You have no ADSL connection but your router is in sync

If the “DSL” light on your router is ON, then this indicates that the router is not in sync with the telephone exchange equipment. If the router is in sync with the exchange equipment, but has no PPP connection, the first thing to try is power down the router for 20 minutes, then power it back up and re-test. The purpose of this is to clear any stale session. If this does not resolve the fault, to confirm whether a router is in sync with the exchange equipment, log into the router, go to its status Status page. For example in a ZyXEL router, go to Status > Statistics. If you have an upload and download speed shown, then the router is in sync.
If you do not have an upload and download speed, then the router is not in
sync.
If the fault is “In Sync but user not logged in”, so the router is in sync, but the user has no connection, the next step is to try connecting using the
BT Test account.
Log into your router and change the ADSL connection username as follows:
(ensure you know your existing connection username/password before making
this change.)
User Name : bt_test@startup_domain
Password : (leave as is)

Note the results of this test, then re-enter your own username and password once again.
Note that you can find your FTTC connection username and password in your account control panel at:
http://account.swiftinter.net/
Under the section: My Services > My Connections
Re-test the connection using your own username. Often, logging in using the BT test account will clear a stale session if that’s the cause of the problem.