|You don't have a sound CARD unless you have a physically removable CARD that installs in a mboard slot - otherwise you merely have a sound chip or chipset built into the mboard.|
You must have the correct sound drivers, and they must be loaded properly.
Realtek makes many different sound chips/chipsets.
The mboard manufacturer, or the brand name builder's web site, has the proper Realtek drivers/software for your model.
There are two main categories of sound chips/chipsets - simpler codec chips, which usually have three ports on mboards, and more sophicated ones that have more than three ports on mboards, often 6 . ALL of them on fairly modern computers and sound cards are AC 97 compatible (it was made a standard in 1997) .
It is NOT a good idea to install drivers for the sound while booting the computer, when Windows "found new hardware" detects the sound adapter, doesn't find the drivers automatically when you have it search for drivers, and wants you to point to where drivers for it are - at least some features of the sound are likely to NOT work properly when you do that (the same applies to many other devices). CANCEL doing that, and after the desktop loads, load the software for the sound using the proper software installation program. If you have already loaded the sound drivers, or the wrong sound drivers or software, un-install any listing for it found in Add/Remove Programs BEFORE you try installing the software.
You can connect the 1/8" plugs for more than two speakers to most more recent sound chips/chipsets.
When the proper software for the sound is installed, there should be an icon for it in Control Panel where you can set the uses for it's ports, and/or a listing for it in your programs list, and/or when you plug into other than the green port on the back of the case, that utility may pop up and ask what are you connecting.
Many of, if not all of, the 1/8" sound jacks have two things they can be used for - one or the other. When you connect more than two speakers, you may lose the default function of a port even if you have nothing plugged into it.