Compaq presario V6000 no internal sound

I have a Compaq Presario V6700 Notebook, with Realtek high-def audio running OS Vista Home premium.

I purchaced in July 08 and no problems at all with it until Feb 09.

In Feb my sound stopped working from the internal speakers. I tried updating and reinstalling drivers for the sound (used correct drivers from Compaq website) and it still didn't work so I have just used the headphones in the past two months.

I am now in a situation where I need the internal speakers to work, so I have tried updating/reinstalling the drivers again and no go. After doing some more research I have tried doing a system restore to before the issue began in Feb and still no sound.
I then did a complete restore back to scratch so I had a fresh new OS and STILL no sound from internal speakers.

I have clueless as to what has happened. I have sound from headphones and if I plug in external speakers they work fine too. The device manager says the device is working properly. The computer has not been dropped or taken apart. Can someone PLEASE help me, I am getting so frustrated and need the sound working by next Wednesday.

Is there a common problem with this happening in this model, or any known faults with these type of speakers? Could it just be a loose wire?

ANY suggestions would be much appreciated, thankyou in advance!

 

Its one of three things

-Dead speakers
-Speaker cable loose
-Powerboard (speaker cable plugs into this)

If you decide to try fix it yourself, here is the service manual and video guide

 

Thankyou for your reply, I will have a read through the service manual and see what I can find. I'll post again later if I can fix it.