First select your audio layer and press "LL"(tap quickly) to open the audio waveform and see if the audio is still there. If it's not, open Window > Audio and make sure you haven't inadvertently set the audio too low.
If that isn't the issue, please upload a screen grab of your comp window for further diagnosis.
Johnny Cuevas, Editor
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.