Timeout error to specific sites: no DNS problem

Hello,

I've got a macbook pro running OS 10.8.5 and a wifi connection. Suddenly I started to get http and https timeout errors with specific sites I've been able to access before:

http://www.tecgraf.puc-rio.br/

https://jira.tecgraf.puc-rio.br/jira/secure/Dashboard.jspa

everything else (facebook, google etc.) works fine. Those specific sites are up and running: when I try my cell phone using the same wifi connection, I can access those addresses. This also mean that there is no DNS or any ISP related problem. Something in my mac is the problem. I tried different browsers (safari, firefox and chrome) and the same problem persists. Even Eclipse (which is not a browser, but has a plugin to access the second address above) can't access them. Already restarted the computer and cleared cache in browser.

Can anybody help me, please?

Thanks in advance.

Leo