I would first connect headphones to the notebook and check if it works on both channels

if the headphones left channel is also absent - i would check the sound settings - depending on the driver you could be accidently switched the left speaker off

if the headphone works on both channesl, the speaker could be unplugged or dead - getting the part might be problematic, but i would check ebay for that

here (click me) is the service manual for that notebook model - it's the original from the hp webpage

I dont think U should open your laptop, as we have arround seven same laptop, including one I am using. but the one speaker problem is common to all of these.

This is some driver issue..

Well the sound driver is bit annoying..my mic stops working now n then..it goes off automatically..every time i got to install the .inf file manually..do u guys ever encountered the same problem?