Hi Matt,
Can you log into your router, under internet connection then connection type, change the connection to adsl / dsl, save and click edit.
Scroll down and see if your broadband username / password are entered. This should be your phone number@talktalk.net
If the details are missing, enter these and save. Remember to put the connection type back to auto when finished.
If the username details are already entered correctly, then this obviously is not the cause,
Thanks
Karl.