Hi,
As you have tried Start-up Repair using the built-in software as well as a USB Stick with Windows 8.1 on it for Repair to no avail, Refresh is the next step.
http://www.eightforums.com/tutorials/2293-refresh-windows-8-a.html
Note
Which Settings will be Preserved
- All user accounts.
- Files in all users' C:\Users(user-name) folders. (ex: Desktop, My Documents, My Music, etc...)
- Wireless network connections
- Apps from the Windows Store will be kept.
- Mobile broadband connections
- BitLocker and BitLocker To Go settings
- Drive letter assignments
- Personalization settings such as lock screen background and desktop wallpaper
- Choices you made during Windows Welcome, such as computer name and user accounts, will not change.
- Network, Libraries, and Windows Update settings will not change.
- Customer Experience Improvement Program settings will not change.
- Windows Error Reporting settings will not change.
- Some drivers may or may not be removed.
Which Settings will be NOT be Preserved
- File type associations
- Display settings
- User settings
- Windows Firewall settings
- App settings
- All installed 3rd party desktop programs (not Store apps). A list of removed apps will be saved on your desktop after the refresh is finished to let you know which programs were removed.
- You PC settings will be changed back to their defaults.
- Installed Windows Updates will be removed.
- Some drivers may or may not be removed.
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But before you do that as you arer worried about your files:
Saving your files:
You can pull the Hard Drive and put it in a USB Hard Drive Enclosure > plug it into another Computer > and attempt to read and copy over your Data that way.
Cheers.