Hi Jordan. I'm Greg, 10 years awarded Windows MVP, here to help you.
UEFI has been the standard for BIOS for 12 years. Installing in Legacy or CSM mode on a UEFI BIOS is like buying a new car and disabling all of the safety and performance features.
The error refers to Windows Boot Manager which is only used by UEFI. I understand you have it set to Legacy, what if you disable UEFI. After getting it fixed I can help you convert it to UEFI using Windows own tool, or better yet you can rescue your files which aren't backed up, wipe the drive and do a gold standard UEFI CLean Install which will never have these kind of problems.
Go to another PC to create bootable media to try the repairs, do a Reset or do the gold standard Clean install. The bootable media is the only repair method that doesn't require a password, has it's own drivers, repair and installation files which often work when Windows or the WinRE Repair Mode doesn't.
To create Windows 10 Installation Media on another PC install Media Creation Tool follow the directions in the middle of the download page here: http://windows.microsoft.com/en-us/windows-10/m.... Uncheck the box for Recommended Settings to choose the exact version and bit rate for the target PC only.
Insert media, boot it by powering up PC while pressing the BIOS Boot Menu Key given here: https://www.sysnative.com/forums/hardware-tutor...
If the media won't boot you may need to enter BIOS/UEFI Setup (pressing key given in chart in link above) to turn off Fast Boot or Fast Startup first.
Choose the boot device as a UEFI device if offered, on second screen choose Repair Your Computer, then Advanced Troubleshoot Options, then:
- Try a System Restore to a point before the problem began, or keep working backward,
- If that fails try Uninstall Updates, working backward until the problem goes away,
- Open the Command Prompt to:
a) run System File Checker: https://www.wintips.org/how-to-run-sfc-offline-...
and DISM Offline from https://www.ubackup.com/windows-10/dism-offline...
b) run a full Disk Check: https://www.groovypost.com/howto/check-hard-dri...
c) trigger Safe Mode with Networking (for internet) or Safe Mode following Option 3 here: https://www.digitalcitizen.life/4-ways-boot-saf... to roll back Updates & Drivers in Windows Update History, update your drivers from the PC/Motherboard manufacturer's website and diagnose further:
https://www.pcmag.com/news/354269/how-to-use-sa...
You can also create a new Local Admin account to replace yours: https://www.isumsoft.com/windows-10/3-ways-to-c...
d) To replace the User account try to enable the built-in elevated Admin account from Option Five here:
https://www.tenforums.com/tutorials/2969-enable...
Boot into this emergency Admin account (leaving password box blank) to create a new Local Admin account:
https://www.isumsoft.com/windows-10/3-ways-to-c...
Sign into the new Account, make sure it works correctly, if so move your files over via C:\Users, when ready delete the old account and change the new one to your MS Account if desired in Settings > Accounts > Your Info > Sign in with a MS Account instead.
- If those fail then go back to Troubleshoot Options to do a Reset. Make it a deep clean reset to set up a new account, with Cloud option to download fresh installation files so it doesn't use old onboard files that may be corrupted.
- If that fails choose Install Now, then Custom Install, then at the drive selection screen delete all partitions down to Unallocated Space to get it cleanest, click Next to let it create needed partitions and start install - this makes it foolproof.
Everything needed to get the best possible Clean Install is here: http://answers.microsoft.com/en-us/windows/wiki.... It is a better install than any amount of money can buy and a great learning experience that will make you the master of your PC because you will learn what works best and how to apply it with your own hands.
- If you have files that aren't backed up you can use the same bootable media to try to rescue your files using these methods: http://answers.microsoft.com/en-us/windows/wiki...
I hope this helps. Feel free to ask back any questions and keep me posted. If you will wait to choose if I solved your problem, I will keep working with you until it's resolved.
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