Hi,
First leave your external speakers unpluged when using the headphones. Is it a desktop or a laptop? Do you have sound from your speakers without the external speakers or the headphones plugged in. If not you may need to reinstall the sound card driver. Go to the maker of you laptop or tower computer maker and go to support tab and then to update software and drivers. Type in the model number of your computer to make sure you get the right driver for your sound card. Make sure you are plugging the headphones into the headphone jack not the mic jack. Now if the headphones have a volume control on the cord check to see if the volume is on and it's turned up some, test them with a cd player or mp3 player regardless of whether they have a volume control or not. If they work with the other players then you should go into control panel, click on sounds and audio devices. Make sure volume isn't set too low or that mute is checked. If mute is checked uncheck it. Click on advanced ( the one next to speaker volume for me), or each advanced button there is until you find a menu that lists laptop stereo speakers if it's a laptop or just speaker setup, under that you should be able see a box that says stereo speakers with an arrow to the right of it pointing down, click on the arrow you should then see more options then scroll down until you see an option for stereo headphones click on that. Plug your headphones in and try them again. I hope they work with one of my suggestions, if not I don't know what else to suggest. You will need to change the setting back again whenever you want to listen to your computer without the headphones
Good luck.
