Patience is a virtue. Just do your best to not take it personally if someone doesn't answer right away. There are a myriad of topics on this site and it may take 1-2 days for someone to respond, for future reference.
Anyway, I don't have a Music Star but I'll do my best from what I know. To pass the auditions, you need to raise skill points and in order to do that, you need to train it by using the training function so that your Tamagotchi can practice its instrument and reduce its stress level. So I'm guessing you can't pass either because you still need to raise the skill points, your Tamagotchi's stress is too high, or maybe both.
Good luck! :kusatchi: