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Message “Missing Operating System” During Boot

When attempting to boot, you receive the following error message:

Missing Operating System
This error message is generated by the MBR code and the problem can have a number of causes.  The most common of these are as follows:
  • The geometry (CHS) setting on the system has changed.

  • No partition is marked active.

  • An unbootable or unformatted partition is set active.

  • The hard drive is failing.
Ensure that the following conditions are met:
  • If the problem is the result of geometry misconfiguration, correct it by setting the Mode (sometimes referred to as the Access Mode) in the system BIOS to Auto or LBA.  In some rare cases, it is necessary to select Normal for this setting.

  • Mark the desired partition active.

  • Run the hard drive manufacturer's disk diagnostics on the drive. Use the most thorough test available.  Below are links to some major hard drive manufacturer home pages:

    Western Digital

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