Hi Ankit,
Are you able to boot to the system?
If you are not having the Windows 8 installation DVD, you may have to create one, boot the computer from it and then perform an Automatic Repair of Windows 8. To create a Windows 8 installation media,
you may refer to the article given below:
Create installation media for Windows 8.1
After creating the disc, boot the computer from the disc and then try the following method to perform an System Restore of Windows 8.1.
Perform a System restore and check.
To perform a System Restore, follow these instructions and check:
a) Contact HPto know on how to change the boot order of the computer. You will have to change the boot device to CD/DVD drive and then boot from the Windows 8 installation disk.
b) In the “Windows Setup” dialog box that appears, set the Time and currency format, Keyboard or input method
and the language to install and then click “Next”.
c) Click on “Repair your computer” from the lower left corner.
d) From the “Choose an option screen”, click on “Troubleshoot”.
e) Click “Advanced Options” in the “Troubleshoot”
screen.
f) In the “Advanced Options” screen, select “System Restore”.
g) Follow the on screen instructions to restore the computer to an earlier state when the computer was working fine.
Now, check if you are able to boot the computer successfully.
Please post back your results for further assistance.