Strange network problems

Hi,

I'm trying to figure out what's wrong with a computer with some strange network problems. From what I can tell, the computer is capable of using DNS - it can find the IP addresses for sites based on the domain names, however, it is incapable of doing more than that. For example, it can resolve google.com's IP address (as well as pretty much any other site) but it cannot load pages or do anything else. This problem seems to affect everything else as well - IM programs, etc..

I've checked the network settings and they are correct for the current college network - automatic IP address as assigned by DHCP, etc., and nothing seems out of place (Given IP is a valid one, Windows is reporting no problems with the connection, tried both with and without Windows firewall). I've even confirmed that there isn't a problem with the actual physical connections and removed some adware/spyware that was there. The strange thing is that it apparently didn't work for a while, then it just decided to work fine for about a week and a half before dying completely again.

Could anyone provide any suggestions about how this might be solved?

Thanks in advance.

 

Forgot to mention:

The computer is running Windows XP SP2 (not sure about Home or Professional - it's not my computer). Also, it is a Sony VAIO, though I am not completely sure of which model it is.

As far as I can tell, there is some kind of antivirus software running, and no firewalls apart from the Windows XP firewall.