Hello roopal_k,
Thanks for posting on the HP Forums!
I understand the computer freezes occasionally. To assist you, I would perform all the solutions in this document: Computer Locks Up or Freezes (Windows 7)
If that doesn't help, then it is safe to assume there is a hardware failure. I would contact HP phone support to discuss your options. You can utilize this website to learn how to contact HP appropriately, based on your region: Contact HP Worldwide
Please let me know if you have any other questions or concerns. Thanks!
Mario