Macbook Air Internal Speakers Not Working, But Headphones and External Speakers Are...

Hi,

I've Macbook Air (Early-2014) 256GB-SSD Model... I'm facing this problem from last two days:

1. No Sound from Internal Speakers

2. No Sound at start up also from Internal Speakers

3. Using external devices or headphones, Everything working fine

I've tried restart it many times, but no luck... In sound setting, in output tab, whenever I'm connecting headphone, sound output device is changing to headphone (type- headphone port) and on ejecting headphone, output device is changing back to internal speakers (type- built in).

What should I do? Help Me...