I cannot see the small tick box to mute the audio on my layer in my project.

Without any info about your system, your footage files and the audio contained in them, your audio preferences and so on we can't realyl tell you much. If the tick box doesn't show up, AE simply cannot access the audio and things there isn't any and there's no way to enforce any of that. You realyl need to fix the respective settings and/ or your files.

Mylenium