2、Inserted an earphone.
1. Depress the volume button; check if volume is too lower.
2. Check whether pressed the mute button, try to depress it again.
3. Turn to another program to see whether it's a single problem
4. Check if it has inserted an earphone.
1.Increase the volume
2.Press the mute button
3.Check the single wire
4.Pull the earphone out