Shooting in the dark here a little but....
Click the little up arrow down on the task bar by the clock and it will show you some extra icons, if you hold the mouse still over any of them for a second or so it will say what the icon is, look for the one that say something like realtek audio manager and click it to open. Once it's open have a look through the settings for audio effects and set it to none (sounds like you have it set to something like concert hall at the moment)
if you can't find the icon down by the clock then look in the control panel as it should be there too.