Start with script languages, python or lua ( whatever is your choice ) to design your game, scripting allows you to iterate quickly for the game mechanics. Nowaday you can always find a game framework for your favorite language. So no language is a bad choice.

I do prefer C, because of a better control over the program flow and memory, but C++ got nice features ( templates and namespace come to mind ), additionnally C force you to write a lot of boilerplate code.

C++ compiler also tend to get a lot of liberty with your code, and all C++ features can make the intent of the code unclear ( object oriented language tend to have unforseen side effects, operator overloading can differ from the initial intent, like "<<" & ">>" over streams ).

What are the OS/Browser combo you are using at school and at home ?

Depending on the browser security, it would not load mixed protocol resources.
You are probably loading the html page directly from the disk instead of a http server.
So to avoid security issues (mostly with untrusted javascript ), your browser will refuse loading remote resources

Let's be honest there and just say that everyone sucks at security because nobody exactly knows how it is working.