Question : Problem: NO SOUND IN DELL INSPIRION 5150 LAPTOP

I AM EXPERIENCING A TYPICAL PROBLEM WITH MY DELL INSPIRION 5150 LAPTOP I AM ABLE TO LISTEN AUDIO WHEN I AM USING USB HEAD SET BUT THERE IS NO SOUND IN EXTERNAL SPEAKERS AND STEREO SOCKET OF LAPTOP WHAT SHOULD I DO .TO BE CLEAR NO SOUND IN EXTERNAL SPEAKERS AND STEREO SOCKET BUT I CAN HEAR SOUND THROUGH THE USB PORT.MY LAPTOP CONFIG IS P4 3.6GH,512MB RAM.40GB HD.I THOUGHT THE SOUND IS DEAD IN MY LAPTOP BUT I DONT THINK THAT IS THE CASE AS I AM ABLE TO HEAR IT THROUGH USB PORTS.I DID INSTALLED NVDIA DISPLAY DRIVERS BUT OF NO USE.

Answer : Problem: NO SOUND IN DELL INSPIRION 5150 LAPTOP

It sounds like a hardware problem.   If the laptop's working fine otherwise, it's not worth replacing the motherboard.   An easy way to add sound is to use an external USB SoundBlaster Live:
http://www.newegg.com/Product/Product.asp?Item=N82E16829102174