In the last 10 days, I came up with two similar cases of laptops being suddenly unable to boot. It appeared that the boot loader was corrupted, making them unable to boot into Windows 10.
They both displayed the following error message:
Your PC needs to be repaired
Error code: 0xc0000034
So, the first step to fixing it is to get a bootable Windows 10 Setup USB (or DVD) from Microsoft.
Next, boot the computer from this USB (or DVD), select Repair your computer click on Troubleshoot and then on Command Prompt.
Once there, you can try the following commands:
In my case however, the last command failed with the error: The requested system device cannot be found
So, after some more digging I ended up doing the following that solved the problem
Still in the command prompt, enter:
Select the PC Hard drive:
sel disk 0
List the Volumes on that disk:
Find the EFI Volume. It’s the one formated as FAT32 with a size of 100 to 200MB. Note it’s volume number to use it in the next command. In my case it was the #2.
Select the EFI Volume:
sel vol 2
Assign a drive letter to it:
Next run the following commands:
cd /d b:\EFI\Microsoft\Boot\
ren BCD BCD.bak
bcdboot c:\Windows /s b: /f ALL
Reboot and you should be OK.