I'm not sure if this is only the school computers being stupid, or if the page is actually down, but when I go to http://plesk.lvcs.net:8443 , you get the Page Cannot Be Displayed screen. It may just be a stupid temporary bug, my school system, or something... but eh.
There are currently no problems with Plesk.
Your school may be blocking everyhting that isn't port 80 or 443. As Plesk requires port 8443, the connection might be blocked by your school's proxy server. I have already seen something like that.