Simply restarting his computer might solve the problem. If not . . .
. . .the fault could be one of two things. Either his PC is not making any connection to the internet, or it's connecting to the internet but not to Tiscali's domain name server (='DNS', which converts 'www' addresses into numeric form).
Ask your friend to enter 209.85.129.99 (instead of a 'www' URL) in the address bar, and click 'Go'. If it's a DNS problem he'll be taken to the Google homepage. (209.85.129.99 is the 'real', i.e. numeric, IP address of Google. Entering it bypasses the DNS). If he still sees nothing, the problem lies directly with his connection to the internet.
If it's a DNS problem, he needs to go into his internet connection settings. It's likely that they'll default to 'automatically assign a DNS'. This should be replaced by entering the actual IP address of Tiscali's DNS. The primary DNS is 212.74.112.66. The secondary DNS is 212.74.112.67.
If it's a problem relating to his main connection to the internet, there's probably nothing he can do about it without the assistance of Tiscali. (It might be necessary to adjust something at their end). Phone 0871 222 3311. (10p per minute. Lines open 24/7).
Chris