I've messed up my system yesterday. On my iMac I have installed OS X and Windows 10 using Boot Camp Assistant. The Windows MBR is damaged and I can't start it anymore. I get a black screen with the error message:

No operation system found

Luckily I can still start up OS X. I'm looking for a way to repair the MBR in the Windows partition. When I start Disk Utility in OS X and click "Check" on the Windows partition, it prints the following error:

Invalid BS_jmpBoot in boot block: 000000

I've already tried to repair it with fdisk, but also when I create a HFS+ MBR it gives me this error. I've tried to figure it out for multiple hours now and nothing seems to work. I do not want to wipe the whole partition because then my whole data would be lost.

The command fdisk can be used to copy the boot code to a destination MBR from some source file or MBR. This source is not supplied by OS X.

One way to write boot code the the MBR would be to follow the step given below.

  1. Insert DVD or flash drive you used to install Windows 10.
  2. Restart the computer and hold down the alt/option key.
  3. Select the DVD or external drive icon labeled Windows.
  4. Open a Command Prompt window by clicking on the following sequence.

    Next
    Repair your computer
    Troubleshoot
    Advanced options
    Command Prompt

  5. Enter the following command. I assume C: is your Windows 10 partition.

    bootsect  /nt60  c:  /mbr
    

Check out the following link Apple support error: Invalid BS_jmpBoot in boot block: 000000

If you can´t restore that way, reinstall the full system.

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