You will either need a full installation disc of Windows 8(.1) or to send it to Asus to have them reload the factory image. Unless they're (Asus) willing to sell you recovery media, which I don't think they do, those are generally the only legal ways to reinstall the OS. You can try cloning another installation over to the laptop, but if it's a completely different computer, chances are that it will blue screen and you'll have instability.
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