You could take it to a repair shop like advised.
Or you could purchase a new sound card and install it yourself but in order to do so you may need an electrostatic kit. It comes with a wrist strap and mat to touch the internal portions of your computer.
These kits could be costly and if you don't know what your doing it could be interesting to say the least-
You can try:
Opening a terminal and bring up the alsa mixer and try muting and un-muting the sound colums and see if that restores your sound. To do this:
1. Open a terminal and type in:
The terminal will open up and the background will be like a dark gray.
You'll see all of the columns that you can adjust. The first should be Master; PCM; and mic.
Mute and un-mute each and raise up the volumes.
When done adjusting all-
[CODE]Hit ESC one time and then close the terminal
If I were you I'd try adjusting the alsa mixer first.
Than see how difficult it would be to replace a new sound card verse's paying (Can be expensive) for services rendered to the computer repair tech-
Best of luck to you