You have integrated audio on your motherboard. Meaning the sound card is part of your motherboard, chances are the drivers are corrupt, or the audio chipset is fried.
The audio drivers for your system are at the following link.
Download the drivers to a directory on your hard drive, Make a note of where you put the drivers.
Next go to the control panel and go to system/hardware/device manager and right click on the audio controller, click on uninstall then reboot your computer. When it reboots, windows will want to install the drivers for a device found. Tell it where you put those drivers and let it install them.