Hard disk replaced,how to get OS back

Farooq Sk

Dec 27, 2014
Hello,I have a lenovo G500s laptop and i got its hard disk replaced under warranty service the old hard disk had Windows 8 and the new hard disk has windows 8.1 trail version . Now how do i get my Original Win 8 back ...or just its key , because i didnt get a Win CD with my lappy. And if possible how can i activate the trail version of win 8.1

Thank you.