Problem trying to use one key recorvery on lenovo laptop

hello everyone im new to this forum so please help me through, i brought a new lenovo G500 laptop 6G ram, 1TB hard drive, 15.6 inch, intel core i5 AMD graphic a month ago and as i was using it then i wanted to update it to windows 8.1 and all of a sudden it became faulty i took it to warranty shop,and the guy stupidly formatted my hard drive and i lost everything including the os so he installed a crack version of it and gave me the laptop back, here's my question can i still be able to factory reset my laptop? cause i think he also formatted the laptops petition, and if yes can you pls give me a detailed guide as to how, i would be greateful to anyone who can help