According to your Everest report, the sound driver is already installed otherwise the device would not be shown (Multimedia:
Audio Adapter VIA AC'97 Enhanced Audio Controller). You would also have a yellow question mark against 'Multimedia Device' in Device Manager if the driver wasn't installed, or a red exclamation mark if it was the wrong driver. If the latter is the case (wrong driver) go to this MSI web-page and use the "Live Update Online" feature which will automatically detect the factory-fitted sound device and offer you the correct driver:
http://global.msi.com.tw/index.php?func=downloadindex
Another possibility is that even though the right driver is correctly installed, the device itself (the sound chip) may have failed. In such cases the solution is to fit a PCI sound-card and disable the on-board chip in the BIOS settings.