It can also be that you put in the wrong time. It needs attention during the morning, afternoon and evening. If you set the wrong time, it will think you're awake when you are asleep or vice versa.
Press B, then hit A+C at the same time, and change your time.
To turn off the sound, hit A+C at the same -time, and it will say:
SOUND?
-> ON
OFF
Select off.