My acer laptop came with the balance all the way to the right, so could be your has came with an off balance setting???
Recently, i have noticed that the left speaker only works intermitantly, i am guessing loose connection.
It would be unusual if the speakers and the headphone jack are both broke, sounds like a setting problem. Make sure the soundcard isnt set to mono if there is a mono and stereo setting, make sure all balane controls are centered, sure you have checked this.
Acer support is very good, sending it back to dabs is one way, ringing acer may save the bother of sending back and getting a new one?