If U bought the PC as it is, just go to the site of your PC manufacturer, type the PC model in the search box and get the sound card driver.
If it's a parts-build PC then find out your sound card.
To find out your sound card go to Control panel under Sound and audio devices and check your Audio tab, under Sound playback , the default device (that's your soundcard)
Or Start>run and type dxdiag and to to sound tab to see your sound card model.
When U find out, go to your manufacturer site to download the driver.
Or, just right click My computer, go to properties>hardware>device manager> and under sound and audio double click your sound card and click update driver on the driver tab while letting it search the internet for your driver.