Sounds like your school is using Malware Inspection with Microsoft Forefront on it's server. Since you are able to access your webpage from outside your school network, I'm almost positive the Microsoft Threat Management Gateway is blocking your access to your server. You are going to have to talk to the network administrator at your school to add your IP to the Malware Inspection "Exceptions" list. Knowing those guys however, you may be out of luck. Sorry couldn't be much more help, but I don't think there is anything that you can do at this point.