Use Speccy or similar to find who made your sound card. Speccy - System Information - Free Download
Best way is to go to the sound card manufactures site and download the latest driver to your desktop. Then,
Go to Start, type Device Manager, Expand the Sound,Video and Game Controllers, On the entry that is there (Realtek) Right Click,Properties, update driver.
When it asks if you would like to go on line or browse your computer, pick browse and go to the file you downloaded earlier.
Once we know you have the latest driver installed it will be easier to help you.