Do you hear sound fine elsewhere (Media Player, iTunes, YouTube, etc)?
In order to ensure you have the latest sound drivers you'd need to know what
hardware you have. If you have a pre-built OEM system such as a Dell, HP,
etc, then go to the support website of the manufacturer, look for the link
to download drivers and software. They will typically have a place to put
in your model number and give you a list of drivers to download.
If you have a custom-built PC from a friend or computer shop, you can check
the Device Manager (Start -> Run -> devmgmt.msc) to see what Sound
controller you have.