Can anyone who plays the clarinet help me?

Okay. I bought my clarinet new an have only been playing for 5 years (Though its a beginner)... I don't think its getting old, but I just thought I'ld mention that. Every little problem I've had with my clarinet my band, marching band, and orchestra teachers have been able to fix. This time that is not the case. My clarinet refuses to play a B (You know, the one that uses all the fingers).. Everything else is fine! Do you have any idea what could be wrong with it? I had 4 teachers do a thorough inspection, none of them knew what had happened... There are no loose screws, leaking corks/pads or anything! HELP!!!!! Marching starts this thursday, and I'm one of the few clarinets that actually plays in marching band, so I need a working instrument...