"Have checked I.P. settings and user name/password are all correct?" You should be using the DHCP server within your router, or have you setup your IP addresses manually?
You did not mention but have you checked the following settings on your router.
VCI - 38
VPI - 0
Encapsulation mode - VCMux
Authentication - Chap
Protocol - PPPoA
Tiscali Primary DNS Server - 22.214.171.124
Tiscali Secondary DNS Server - 126.96.36.199