Blocked, but don't have proxy or fw...

Hopefully someone here can help me out, because no one else has been able to. For some reason I seem to be blocked from certain internet programs, almost like I have a firewall up (which I do not). I can access browsers fine, plus AOL IM and Weather Bug, but I am unable to upgrade anything (cannot connect to server), can't connect to P2P programs, and, my biggest problem can't play Counterstrike! I am running through a school ethernet, and they have no firewalls up that would be doing this. I have no clue at all. I was sure it was my school, but I called them and they say they have no fw up, and my roommate has no problems. I'm running 2k pro. Any help would be greatly appreciated. Thanks!
-Josh