Accidentally Reset Windows

[MrDingleFart]

My PC wasn't working properly so I did the hard restart 3 times to bring up the boot settings so I could reset my PC, I did the option that said it will remove everything that wasn't on the PC since the start such as Personal files, and it said I can restore them whenever I want. I assumed by doing this it would leave the OS and just delete everything else, but now I'm stuck on the bios screen that says "An operating system was not found. Try disconnecting any drives that don't contain an operating system. So if there's a way I can get my OS back without paying for another one can you please help. Ps I also don't know the key because I baught the PC off someone else

 

[Colif]

Full resets can get carried away and wipe all signs of Windows.

on another PC, download the Windows 10 media creation tool and use it to make a win 10 installer on USB

After a broken reset, I would suggest a fresh install
change boot order in BIOS so USB is first, hdd second
boot from installer
follow this guide: http://www.tenforums.com/tutorials/1950-windows-10-clean-install.html

when you reach the screen asking for licence, click "I don't have a key" and win 10 will continue to install and reactivate once finished

On the screen where you choose where to install win 10, if it gives you an error about GPT drives, delete all the partitions on the hdd and press next. If it still gives error, cancel out of the installer and restart PC and start installer again, it will accept next on that screen this time (some PC just need a restart here)

the licence should be tied to the PC so once you install Windows 10 again it should auto activate. Licence info is stored on MS servers so I guess once PC is installed you will find out if you have a licence or not