No no no - if considering reverting to Win 8- if it's possible with this failed installation, then as per my previous post
1. Boot your PC from Win 10 bootable medium
2. Click repair your computer.
3. Navigate through the options as per the ttuorial I quoted for you.
Forget your Win 8 reset disk.
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Ok, if there's not much on it, then I strongly recommend you do a clean install.
(I amended my previous post to give you a possible - but not certain- option to recover your old Win 8 build).
Here's how to do a clean install:
Download Windows 10 ISO File Windows 10 Installation Upgrade Tutorials
Create Bootable USB Flash Drive to Install Windows 10 Windows 10 Installation Upgrade Tutorials
(or use a DVD)
Now, if you have a retail license for Win 8, then - during the original free upgrade period- you could do this easily:
Clean Install Windows 10 Windows 10 Installation Upgrade Tutorials
Now, however, officially that's not possible, although you can try it.
If, however, your license came with your PC - an OEM one- then you would have had to upgrade - or buy a retail license for win 10.