Confuddling - BTW, I've just checked www.apple.com and it's up and running.
Let's be clear here, you have internet access to certain websites but not others, and that your friends are happy?
Can you (in Terminal) ping www.apple.com ? You should get;
PING www.apple.com.akadns.net (22.214.171.124): 56 data bytes
64 bytes from 126.96.36.199: icmp_seq=0 ttl=238 time=154.829 ms
64 bytes from 188.8.131.52: icmp_seq=1 ttl=238 time=152.671 ms
64 bytes from 184.108.40.206: icmp_seq=2 ttl=238 time=155.570 ms
If not, then can you ping it by the IP number (in Red above)?
Are you the only one in the building connected by ethernet cable to the router?
Are you sure you are all using the same DNS server (the ISPs would be favourite)?
Does your router have any url blocking software?
Have a try and revert if still problem.