sound is completely gone. can sound card reader be replaced

Run Audio MIDI application. see what it's set to . Should be Internal speakers. Go to Sound/ Alerts under System preferences-see what it's set to play the alerts/sound through...sometimes it goes a bit wonky. try zapping the pram/resetting the SMC/PMU. How to do this can be found on Apple's support page for your MacBook pro or if you can't wait, like me, google, yahoo, etc might be helpful. Also , if you hold down the option key and click on the speaker icon, it'll show you all sound inputs and outputs. IF after doing that you still don't hear any sound, from anything, then maybe it's time to take it in for repair. and no, I can't tell you for sure if you can replace/repair the sound card. It's probably part of the logic board, and as such, only the repair shop can tell you for sure...

well, it's a start anyways

John B