OK.
Get hold of some cheap earphones (e.g. for a quid in Poundland). Plug them in to the 'speaker' socket. Find any sound file on your computer's hard drive, such as the sound of Windows loading. (To do that, run a search for *.wav, which will find all files in the WAV format). Double-click on it to get it to play in Windows Media Player (or whatever else your default media player is). If you hear the sound through your earphones, there's a fault with the speakers. If you don't there's either a fault with the sound card (or onboard sound) or with a driver.
That might not solve your problem but at least it will tell you where to start looking for a solution. (NB: If you try that experiment, please don't try to use sounds from a CD or from, say, Youtube. That could introduce possible problems with your optical drive, with your web browser or with Adobe Flash. It's important that you should access sound files directly from your hard drive).