If when you start your Windows 10, Windows 8 or Windows 8.1 computer, you receive a Your PC needs to be repaired error message, then Then this post may be able to help you resolve the issue.
A required device isn’t connected or can’t be accessed
The drive where Windows is installed is locked. Unlock the drive and try again.
If you try to Reset your PC you will see the following message:
Unable to reset your PC. A required drive partition is missing.
The cause for this error is normally a corrupt MBR or BCD file. To resolve this issue, there are a few things you may want to try.
1] Boot into Advanced Boot Options. From the WinRE screen, select Troubleshoot > Advanced options > Command Prompt. Run Check Disk using CMD. You may use the chkdsk /r command.
2] If a system file required for booting up has become corrupted, running System File Checker may help you.
3] You may be required to change the active partition using diskpart. An Active partition is the one that your BIOS detects is the one that will start your computer.
It is important to note that changing Active Partition wrongly may make your computer unbootable. So do not by mistake, mark a partition as Active, if it does not contain the NTDLR loader for your operating system.
To do this, enter the following commands:
Now select the disk – it will typically be Disk 0 – and set it as the Active disk. Assuming it is Disk 0, the commands become:
select disk 0
Now list the partitions using:
Assuming your partition number is 0, the command becomes
select partition 0
To make it the Active partition, type the following and hit Enter:
4] Repair Master Boot Record. It is one of the effective troubleshooting steps, to fix boot issues, and will hopefully help you fix the problem.
Update: Please see boozi‘s comment too, below.
Some other links that may help you someday:
- How to Convert MBR to GPT Disk
- Windows 8 fails to boot; Automatic Repair, Refresh, Reset PC also fail
- Operating System Not Found
- Bootmgr is Missing.