You haven't said what device you have, so I can only refer to a couple of things on my HTC One that would affect the alarm sounding. They are both in Settings-->Sounds.
Firstly in Volumes, the alarm sound has its own slider control which needs checking, and secondly in Notifications and Alarms, the alarm has its own list of sounds to choose from which includes 'Silent'.
If your device is different to this please resubmit your question and include device details and someone will be able to help you.
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.