Alright, not sounding good at the moment if the headphones are doing the same thing. Guess at this point the speakers are fine. If you have anywhere else you could try them to be sure (TV headphone jack)
Your motherboard is using Realtek sound,
http://www.realtek.com.tw/downloads/downloadsView.aspx?Langid=1&PNid=24&PFid=24&Level=4&Conn=3&DownTypeID=3&GetDown=false (Check the agree box and download the version 32bit/64bit for your operating system)
Try reinstalling their latest driver, if it still isnt working then probably have faulty audio connection somewhere on the motherboard in which case buying a sound card would be an option to consider and disable/ditching the onboard sound altogether.