Cannot open some sites

[petermeachem]

Strange problem with an XP SP1 pc.
I can open some web sites but not others. The situation is exactly the same with Firefox and IE. Another pc with, as far as I can the same settings, can see any site. Both connect via a 3com router/modem/firewall to Plusnet.
Both have Norton Internet Security, same version.
The duff pc can open hardly any sites, bbc is ok, grisoft is ok. I suspected at first spyware or a virus but Norton and something called Spyware Doctor come up clean. I couldn't get to spybot or hijackthis and didn't have a copy with me so there could be something.
Where should I start looking?

 

[smah]

If this is reliable & repeatable with both browsers, look at your hosts file. See if the sites you can't get to are listed as 127.0.0.1

 

[petermeachem]

Sorry, forgot to say, the hosts file is quite normal and standard.
It is quite repeatable too.

 

[smah]

I believe that NIS sets up some sort of 'proxy' service. That would by my next place to look. But I can't say much more about that because I don't use it. Maybe the proxy configuration is wrong, or maybe somehow it just got corrupted (I don't know how it works, so I'm just shooting in the dark here). If possible, disable NIS entirely and test.