Why can't I connect to proxy server?

[이현우]

Up until recently, I have been able to connect to a proxy server to bypass Fortiguard on my school network. Suddenly, I cannot connect to the internet through the proxy. I can, however, send/receive messages through IM apps on my desktop without any problems, so obviously there is some kind of connection present. What do I need to do to fix this issue? I am using Chrome, which I know probably has nothing to do with it, but still. And if you give me that crap about "Bypassing your school's filtering software is not the right thing to do" or "That's against the rules!", etc. then just don't even bother in answering. It's annoying. Please, only people actually willing to help!!!!
It's Windows 7, 64-bit, with admin. permissions