edit: it's fixed now! i managed to find this thread which is the exact same issue i was having (minus the HDMI cable) and following these instructions for a hard reset fixed the problem. we have volume, we have output controls, and now we know what to do if it happens again.

my daughter uses a chromebook we bought for her last year. usually she keeps a pair of headphones plugged into it to listen to music & watch videos. this morning she says she was watching a video on youtube, no problem, and when the next video loaded there was no audio.

her chromebook seems to be locked on mute - when i move the audio slider, it still shows the mute icon. i've made sure bluetooth is turned off (there doesn't seem to be a way to stop it from turning on when she reboots, but as far as i know she doesn't have a bluetooth device synced to it anyway). when i click the gear icon next to the slider, i get a screen with the output settings for about half a second and then it switches to a screen that only gives me 3 toggles, for login sound effects and the like.

i've tried using guest mode, and i've tried logging in to my profile in case it had to do with her account being a minor, but i still couldn't unmute the audio in either of those circumstances. what am i missing? why would the audio just shut off in the middle of watching videos and not let me turn it back on? am i going to have to factory reset her chromebook to get the audio back?