What actually went wrong and how to prevent this from happening to you:
Originally Posted by NavyLCDR
Solution #1 (slightly longer & requires two drives, but worked perfectly): Image your C:/ partition using Macrium, format & reinstall Windows (without any other drives connected) which allows Windows to create all the correct partitions, and restore your image back onto just the new C:/ partition. Instructions.
Solution #2: manually add the EFI partition that was missing. A normal clean install creates 4 partitions, but I only had two: I was missing the crucial EFI and the non-essential recovery partitions. Instructions.
-- original post below --
Hi! I had Windows 8.1 Pro x64 on an old hard drive (250GB). I installed a new hard drive (500GB) and did a clean install of Windows 10 on the new hard drive (using my Win8 CD key).
It worked fine for two weeks. I never booted into Win8 again, but every time I booted, it gave me the option of Windows 10 vs Windows 8. Always picked Windows 10.
Then, last night, I wanted to use that old hard drive with Win8 for storage. I formatted it via Windows and secure erased it (via gparted on a live USB--this did require disabling secure boot, but I re-enabled it after secure erasing). After rebooting, Windows 10 won't boot: "no bootable devices detected".
The hard drive with Win10 is still recognized in the BIOS, no problem. But, even in the BIOS, it's not seen as a UEFI bootable device.
What I've tried so far:
1. Startup Repair (using the Win10 USB live installer tool thing) -- "Startup repair couldn't repair your PC." Log file is blank, sadly.
2. bootsect /nt60 C: /mbr -> it works successfully, saying "successfully updated NTFS filesystem bootcode" and "bootcode was successfully updated on all targeted volumes", but I still can't boot.
3. bootrec /fixmbr -> completes successfully, still can't boot.
4. bootrec /rebuild bcd -> finds the Win10 install, I select it, and then it says, "the requested system device cannot be found."
I ran diskpart and here's what I'm looking at:
That makes me worried. Should it be Gpt? It shouldn't, right?
Disk 0 - Online - 465 GB - 0 B (under free) - blank (under Dyn) - * (under Gpt)
Shoot, this looks bad, too, right? Shouldn't I have 4 partitions? I did a clean install and it was with "raw unallocated space". But, somehow, only two partitions.
Partition 1 - Reserved - 16 MB (under size) - 1024 KB (under offset)
Partition 2 - Primary - 465 GB (under size) - 17 MB (under offset)
Volume 1 - C - NTFS - Partition (under type) - 465GB (under size) - Healthy (under status) - blank (under info)
Am I SOL? Is this unsaveable? I had no idea it was so bad to format a hard drive I hadn't even booted from in 2 weeks, but maybe that Win8 hard drive was handling some UEFI booting responsibilities that weren't passed onto the new Win10 clean installed hard drive.