my sister bought some speakers with a sub to enhance the sound.her son tried to hook them up.now there is no sound coming out anywhere.
Need more info.
Worth checking that the speakers are connected to the right output on the sound-card (built-in in this case ?) The main line-out on most cards is the green socket. Then go into audio options and check the levels are adjusted correctly. I can't really offer you anymore that that until you give me more information, are you using surround ? what type of leads are there from the speakers to connect to you're computer ? and does your on-board Realtek sound support surround ?
If you are not sure how to describe how everything was hook up, take pictures of speakers and the back of the computer where the speakers connected. This will give us better information to be able to help you properly.
After you've taken the pictures, one other thing to try is to connect the speaker system to an MP3 player, if there's sound, then it's just a proper PC setup may be needed.