Sir, I'm just newly employed, my boss ask me to test the audio but it doesn't work, I thought it's just because the system is muted. But when I tried to fix the volume an error pop-up says that "there is no mixer devices available" I look at the computer of my co-worker because her audio is working and I checked out the drivers, it has NVIDIA Network Bus Enumerator but mine don't have it, ,, What I should do? Do i need to install it too? I am using Windows XP 2003 32 bit. Thank you in advance.

What is your computer manufacturer, go to their websites and try installing the lastest audio driver.

It could be that your speaker wasn't connected properly to your computer OR your speaker already broken.
Ask your co-worker to borrow their speaker for a while and test it on your computer. If fail, follow Jingda's step by visiting NVIDIA support site if your computer is the same spec as your co-worker does...