Have you tried connecting your pc,laptop straight into the broadband connection, without the router ?
Agreed, I had the same problem, in the end I phoned BT to check my phone line and it was static on the line and they fixed it for free.if you can not get online with ANY pc on your network - i suspect you have bad noise (SNR) on your line. check ALL your dsl filter(s) AND contact your isp and tell them to run a line test... they should have you back in binary business in 15 minutes..
P2E