A few times over the years I have had problems where a web site was simply not reachable from my place... On any computer.
Once for about a year, I could not get to nvidia.com. Not even by using the raw IP address. Not even by telneting to port 80. It was a black hole as seen from Mac, Windows, and FreeBSD.
Because it happened to all computers on a variety of OSs I decided it had to be an ISP issue. And rather than try to explain it to ISP tech support, I just lived with it until it cleared up by itself.
Try the things that people are suggesting, but in the end it may not be a problem on your end.