Why can't I see special characters on my computer?

I just got this computer, it has Windows XP software and special characters show up as a box with two numbers in it (e.g. a 55 above a 32) but all characters show up on my other computer that uses Vista software. How can I make the special characters show up? I already tried going to view>character encoding>auto detect>universal and im using unicode (UTF 8) and im using Firefox.