This steps are for operating system with Windows 7, however, the steps are same for all Windows operating system.

1 )Copy and paste the following link to your internet browser.

http://support.hp.com/us-en/document/c01867418#AbT3

2) Under the 'HP PC's performing an HP system recovery' heading, you may see 'Steps to follow for Recovery from the startup screen (during system boot) OR when unable to boot to login in screen' , click on it.

Please follow the instructions under it.