Sony VGN-FS550 - Manual (Page 177)

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.
 Make sure the speaker volume is not muted and is loud enough to hear sound. Use the Fn+F2 keys to toggle the
mute option on and off, and use the Fn+F4 keys to increase the volume.
 Make sure the sound feature on your computer is enabled. See Enabling the sound for more information.
 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.
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