How can I downgrade from Windows 10 to Windows 8?
If your scenario is that you have installed Windows 10 over Windows 8,
and you have kept the resulting folder C:\Windows.old, then you can use it to
return to Windows 8. This was always possible in the Windows 10 Technical Preview.
This is the procedure :
- In the Windows 10 Start menu select Settings
- Click Update & Security
- Under "Go back to a previous version of Windows", click Get started
- Enter something into the "Why are you going back?" screen
- Click Next and wait, as this will take some time
- You will need to have your password to Windows 8 once the process is finished.
On one version of the Windows 10 Technical Preview, the "Why are you going back?" screen is replaced by a "What you need to know before you go back" screen, where you click on "Go Back" instead of "Next".
You may find that the shortcut to Windows Explorer in the taskbar has stopped working. To fix, right-click the icon, unpin it from the taskbar, then search for Windows Explorer in the Start menu and drag it to the taskbar.
This is explained in detail with screenshots in the article : How to downgrade Windows 10.
If you have deleted the Windows.old folder, a clean install of Windows 8 is in my opinion probably the only remaining option.
Are you in the position to reformat it? Burn the .iso to a CD, pop it into your computer and restart. When you're in the BIOS screen you should see an option such as 'press F12 for boot options'. Hit the key it tells you to press and boot from the CD-ROM.
Then run through the settings to reinstall Windows 8.