Since you've formatted your PC, it's best that you install your chipset drivers.
They include audio drivers for your onboard sound.
Go to: http://www.nvidia.com/content/drivers/drivers.asp and select Platform / nForce drivers in the first box. Then select the nForce 4 chipset depending on your system, in the second box. Then select your Operating System in the third box. Click Go to download your chipset drivers.
When it's downloaded, run the installation package.
Oh...and about getting a new soundcard, the Creative Sound Blaster Audigy 2 ZS Soundcard will certainly woop your onboard audio...!