Unable to hear sound in dell inspiron 15r

Hi,

I bought dell inspiron laptop 2 days back and i am facing problem with my microphone. When i am having video call on gtalk i could able to hear other person's voice when i am using head phones but when i am not using head phones i could'nt able to hear other person's voice but they can able to hear my voice. Please help me out to resolve this.

Raj