I am wondering if it's a DNS nameserver issue.
Can you ping sites by IP address, try ping 163.244.64.253 (which is www.dell.co.uk)
If that works then I guess that your /etc/resolv.conf file is in a poorly way Post the contents of that file here so that we can take a look.
If the ip ping works then can you type nslookup and tell us what it reports back as the default server and address
If the ping is not working can you post the results of ifconfig (run as root) whilst you are connected with the fault in question.
Regards
Wayne