My highschool's home page won't open on either home desktops or my laptop?

I have this big ignment that I need to do and the only way I can finish it is if I go to my school's webpage, then go to my english teachers person page within the school's site. The website (petoskeyschools.org) seems to work on any other computer BUT all of the computers in my house. I don't know a lot about computers and it might be my firewall, but I don't really know how to go about changing the settings to allow the website. According to a description of petoskeyschools.org, it's content type is "text/html; charset=utf-8" if that helps at all. I don't know what to do! This site used to work no problem on my home computers but now it just says "Safari can’t open the page because the server where this page is located isn’t responding." Please help! I'm on a MacBook Pro and my desktops are both Windows XP. Thank you soooo much!!