Windows 8.1 activation - Hard disk replaced

Hi,
I am having HP pavilion sleek book laptop and it was having Windows 8. Recently the hard disk got crashed.
I have replaced it with new one and installed windows 8.1 from Microsoft site. Since it is EOM based, Windows didn't get activated. Unfortunately I don't have recovery disk and HP asking too much money for providing the recovery disk.

Can you please suggest how to fix the issue.

Thanks in Advance...

You will need to extract your Windows 8 OEM key and activate with that.

http://www.eightforums.com/tutorials/27129-product-key-find-windows-8-a.html (option 5 will backup you key for future reference)