|"...Realtek sound card"|
"..Realtek 5.1 compatible soundcard...."
The term CARD is frequently mis-used. It's NOT A CARD if it's built into the mboard! A CARD is removable and is installed in a slot on the mboard inside the computer case.
Onboard sound is a sound or audio adapter or a sound or audio chip or chipset, but it's NOT A CARD!
Intel has pretty good support about this subject.
Troubleshooting audio issues
1. The most frequent cause of a problem like yours is the person has not installed the software for the sound adapter correctly.
DO NOT install the drivers for anything Windows detects while booting, when you allow it to search for drivers and it doesn't find any, and it then wants you to supply the location of where the drivers are, BEFORE the proper software for the device has been installed in Windows, unless the software installation directions tell you to do that.
In the case of software for a sound adapter, usually you NEVER do that - if you do that, the software will probably not install properly.
If you DID do that, go to Control Panel - Add/Remove Programs and un-install the software for the sound device, and install it again the right way.
2. The second most frequent cause of a problem like yours is the person has installed software for the wrong sound chip or chipset. The software found on the mboard maker's or brand name builder's web site for your model, or that is on the CD that came with the mboard is, the correct software.
NOTE that you must have the main chipset drivers for your mboard loaded before you install the sound software, otherwise the sound software may not work properly.
E.g. the sound may not work after the computer has gone into Standby mode and you then wake up the computer from that mode. In that case, it you Shut Down Windows and then re-boot the computer, if the sound was working before, it will work.
For the DG31PR, these are the main chipset drivers you need to install. If you're not sure whether they have been installed, download this and install it - usually it does no harm at all to install them even if they're already been installed.
If the sound software has been installed properly, if the sound chip or chipset is capable of supporting more than one pair of speakers, there is a program you can use to specify which sound port is for what when you connect more than asingle pair of speakers. In this case, there is a Realtek icon in Control Panel for that.
It may pop up automatically when you connect speakers to other than the green sound port and ask you what device you want that port to be for.