Why is there no sound coming from Windows Phone 8?

[WPCentral Question]

Only the vibrate function works. This is a replacement phone, just arrived

 

[Laura Knotek]

Which phone is it? What OS version and firmware is installed?

Does it play any sounds if you listen to music/watch videos, or is it just ringtones/alerts that don't play sounds?

Do you hear sounds using headphones?

 

[Funky Cricket]

Ditto to above, details matter.
If no sound without headphones, but sound with, the switch maybe stuck, try plugging and unplugging your headphones repeatedly a few times.

Otherwise, it depends on what is happening. Please try to elaborate.