|Do you have the volume control on the sys tray?|
If so make sure the sound isn't muted or reduced to zero. If its muted there will be red X on it. If there is no volume control, then it would seem your drivers need reinstalling. The model you quoted isn't the number needed if you are going to install drivers. The number you need is usually on the screen surround and will be VGN-xxxx. It is this number you will need if you need the sound drivers.
Computers... designed to entertain,help with work but most of all to frustrate you!