Go to the computer manufacturers website. Look for -> Support.
It may state Support & Downloads. On the Support page, type your computer model name and model number in the search box. Click on the down arrow to the right of the box, or it may have -> Go.
Choose the Operating System you're using.
On this page look for Drivers & Software Downloads. Click on it. Now click on the drivers you need, and download them. Click on Run, and click on Run again. Ignore the Microsoft 'Squawk Box'.
After you have downloaded and installed all your drivers, restart your computer.
Or, go to the motherboard manufacturers website, and enter the model number of your motherboard in the appropriate box. Click on go, to the right of the box. Click on Drivers downloads.
Now, if you don't have the CD that came with your sound card, go to the soundcard manufacturers website. Enter your soundcard model name and number. Look for the drivers.