Best answer by Mathis
If you've uploaded more than 180 min of audio, that means that you have exceeded your quota - some of your tracks become hidden, and you cannot upload new content.
You can either
a) delete some of your tracks to make space for new uploads
b) upgrade your account subscription to Pro or Pro Unlimited to get more space to upload - any hidden files will be reinstated automatically with all of their play counts & comments, too.