Why can't I get on a certain website?

Hey, i'm a moderator on a fish forum online, but for a week and a half I can't get access to get on the site. I haven't been banned from it, because I can log in on it at my friends house. I use the internet called Safari and I also have a mac computer, but i've also tried Firefox, and I still can't get on the forum. I have also tried getting on the forum on my dad's, and my brother's computer and still can't get on it. Any ideas?