After formatting my system i installed windows 7 but unable to hear sound using earphone.
You gave no system information at all so it is impossible to point you to an exact link.
Your motherboard maker will have that driver as well as all other drivers for any supported operating system.
You will need your motherboard model then go to the makers site. The page for your motherboard should have all drivers relating to your board available for download.
Retrieving data ...