Unable to access sites

I had a problem with the site www.ibest.com.br, for a few months the site did not appear at all in IE, or any other browser. Even with SP2 installed. Now, since last 19/09, I am not able to access www.orkut.com and www.pop.com.br, all I get is the bellow. But the Ibest site, is working fine now, I have tried everything in the help page, but nothing worked.
Can you help?

The page cannot be displayed
The page you are looking for is currently unavailable. The Web site might be experiencing
technical difficulties,
or you may need to adjust your browser settings

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http://search.msn.com/dnserror.aspx?FORM=DNSAS&q=www.orkut.com

We can't find "www.orkut.com "

You can try again by typing the URL in the address bar above.
Or, search the Web:

Go to MSN Search to see complete results for "www.orkut.com ".

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Did you intend to go to one of these similar Web addresses?
www.orckit.com
www.okit.com
www.oru.com

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You can also visit one of these related Web sites.
Orkut
Check availability or register the domain name 'www.orkut.com'.
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http://www.orkut.com/ is Under Construction, at least that is what I get.

 

I’ve tried a different approached this weekend, I turn off all security in my PC, win firewall, mcafee internet security and firewall and AVG. Then I try the URL that I was having trouble, and there they were, I had access to them (Orkut and POP), so I started to turn back on, one by one, to see which one would give trouble again, and find out it was the Mcafee firewall. I still don’t know why it was blocking the url, but, after I look everywhere in its settings, and did not find any indication of the sites in it, I decide to get the IPs from the sites by ping, and include them in the Advanced task, Block IP addresses, and them unlocking the IPs. Well, it worked, although I think it is stupid to have to do that, since it was working fine before, but why argue now, it is working. So, thanks to all the help given.

Brgds
Ricardo