can't get audio to work

I've just reinstalled my pc, and after installing all the related drivers I still can't get any sound. Searched through a few threads here and have tried a few of the suggested ideas and no luck. I re-installed Windows again to start from scratch. Installed motherboard chipset first, then MS UAA drivers, then audio drivers, still doesn't work. I've done a format and re-install before with no problems using the drivers from the original CD that came with the motherboard (which I lost since). I got all the newest drivers from the Asus website and now am having trouble.

System spec:
Intel Core2 Quad @ 2.4
Asus P5K SE
Nvidia 8800 GT 512mb
Windows XP SP2

I've checked that on-board audio is enabled in BIOS, the audio drivers are showing up fine. When I go to Control Panel -> Sounds and Audio devices -> Audio tab, everything is showing the Realtek Audio Output (which I'm guessing is what it's supposed to be showing). Double checked everything is plugged in. Even checked that my speakers are working on another computer.