I install Yosemite, but i got a problem with the sound it dont work, what can i do?

Sound – No Sound After Upgrade (2)

Sound – can’t hear sound from speaker - Yosemite

Sound Levels - Troubleshoot

Sound – Troubleshooting Internal Speakers

Try cleaning out the headphone jack and then insert a headphone several time. Sometimes the jack gets stuck.

Sound problems

In the Terminal, type that:

sudo killall coreaudiod

And in the sound preferences, make sure your internal speakers (and not HDMI or other device) is selected.

Other resources:

http://www.iphonetopics.com/no-sound-after-upgrading-to-os-x-yosemite/

http://betanews.com/2014/08/26/how-to-fix-disabled-audio-in-os-x-10-10-yosemite- beta/