Troubleshooting MBR Problems

Common issues related to a bad or missing MBR

"Operating System Not Found" or "Missing Operating System" at boot time Summary: Upon starting your Windows based computer you receive the error message that the operating system is missing or not found. This error typically indicates a corrupt or missing MBR, or could also indicate that no active (bootable) partition exists on the hard disk. In any case, the BIOS is unable to transfer control to a valid boot record and displays this error message before terminating.


  • Step 1: Run MBRWizard to determine the problem. See How can I see my disk information? for assistance getting this information.
  • Step 2: Is there an Active partition on the disk? If not, you will need to identify a primary partition to set active from the previous step, this is typically the first partition on the disk. Note the position (Pos), then jump to How do I set a partition active? for detail on performing this step. Make certain to replace the partition # in the example with the partition # you want to set active.
  • Step 3: If the problem persists you probably have a corrupt boot loader, which is the piece that turns control over to the NTLoader to continue booting. In this situation we need to repair the MBR, see the sample instructions How do I repair the MBR? which will replace the boot loader code with the original code installed with Windows.
  • Step 4: If the problem still exists, check the BIOS settings, making sure the hard disk is being properly recognized. Other possible causes may be a bad hard disk, or perhaps Windows (or other operating system) is not installed.

"NTLDR is Missing" at boot time Summary: Upon starting your Windows based machine you receive the error message that NTLDR is missing. This error indicates one of several potential problems, but frequently indicates a corrupt or missing MBR.


  • Run MBRWizard in repair mode, this will lay down a new XP boot record, while leaving the partition table untouched.
    If the problem still exists after repair, you can find additional information on this problem here.