You shouldn't have changed the mac of the router to that of the modem- reset that back to it's default.
To ping, open a command prompt (start -> run -> cmd ) then type
ping
www.bbc.co.uk and see if you get replies
then type ping 212.58.224.121 and see if you get replies there.
If you don't get replies from either, type
tracert
www.bbc.co.uk -h 5
and post the results back here.
EDIT: mac address filtering is a security setting which will allow/deny listed mac addresses access to your network. Oh, and once you get your network running, setup some security!!!! -
http://www.cableforum.co.uk/board/article.php?a=12