Try calling your ISP with the problem. I admin a network at my job and sometimes there are just websites that despite everything working correctly, are unable to be reached. You may just have trouble getting the connection.
Of course, this is last-ditch. I imagine there's something brutally obvious that we're all missing, which would stink.
Also, un-install completely, ensure all vestiges are removed, and re-install. Make sure if you're torrenting that no pieces were lost, or just download the entire package .exe style. Ensure you're running the Linux version or the correct Windows (32 or 64, always 32 if you don't know), etc.
you get the point.