Apple Logic Pro /LogicExpress Discussion

I'm due to have my first performance tomorrow, using Logic, and  
I've just lost all the sound. Please, can anyone help me work out  
what I've done. All the Mute indicators on the tracks are flashing on  
and off. I can play individual tracks on solo, and if I solo them  
all, the whole thing plays, but without soloing them all, they go  
back to mute. What on earth have I done?

Thanks in advance for your advice

Andy B