We are going to need a lot more information in order to help you.
Check out that link for what is useful. At the very least, OS version, exact version of AE, what kind of audio files you're using, a screenshot of your full preview panel with the settings revealed for the preview shortcut you're using, a screenshot of your audio hardware preferences panel would be good. Do you see waveforms when you select your audio layers and press LL? Do you get sound when you play them elsewhere (like Premiere)? Etc.