Sony VGN-A140P - Manual (Page 273)

Why can't I hear sound from my speakers?
 If the computer is using battery power, make sure the battery is properly inserted and is charged.
 If you are using a program that has its own volume control, make sure the volume control is properly set. See that
program's help guide for more information.
 Your speakers may be set to mute, the volume setting may be too low, or the audio option may be disabled. See
Adjusting the sound and Enabling the sound for more information.
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