Note: If you have no audio/ sound at all, you should see the guide here MacBook Pro No Sound in Windows 7
1. If you plugin external speakers or headphones in your audio jacks, you hear the sound, but the internal Speakers do not work.
2. You may be having a unibody/ Macbook Pro 13/ Macbook Pro 15 or any other screen size.
This happens when the tiny tabs inside the audio jack are bent. The problem that there is a switch in the jack that tells it if you have a mini headphone plug or an optical plug plugged into the headphone port. The problem is when you remove the plug, the jack doesn’t know that headphones are removed. This disables the internal speakers and you see digital out instead of internal speakers in the speaker conrtol panel.
There are a few possible ways to solve this.
1. Plug and unplug your earphones several times inside and out the audio jack. Plugging and unplugging the earphones may get it working for a while but it won’t last forever. The repair is warrantied, and involves replacing the left IO board. Parts and labor are covered, and the repair should take about 1/2 hr to perform.
2. Use a cable tie/ bobby pin/ plastic tipped Hair Pin; gently prodding all the way down the audio jack on the left side.
Hopefully any of the above two hacks will solve the problem. There is a risk that you may damage your audio jack. So better check your warranty before you try any of this stuff. If it does not work for you, do let us know. Good Luck!