Windows 7/8.X/10 - Installation Media creation

If you have necessity to reinstall your operative system on your pc but you are unable to find original installation media you can easily refer to following Microsoft article.

Make sure you have:

1. Your Windows product key (xxxxx-xxxxx-xxxxx-xxxxx-xxxxx). 
2. An internet connection.
3. Sufficient data storage available on a computer, USB or external drive for the download.
4. A blank USB or DVD (and DVD burner) with at least 4 GB of space if you want to create media. We recommend using a blank USB or blank DVD, because any content on it will be deleted.

https://support.microsoft.com/en-us/help/15088/windows-create-installation-media