Troubleshoot Master Boot Record Error Messages - dummies

Troubleshoot Master Boot Record Error Messages

By Dan Gookin

A host of errors requiring your troubleshooting attention are associated with a bad, corrupt, or missing master boot record, or MBR. These error messages appear when the computer starts — obviously, before the operating system is loaded.

The MBR is arguably the most important part of the hard drive. It’s the first part of the first physical hard drive in your PC. The MBR contains two vital items:

  • A map, or partition table, describing how the hard drive is divided into smaller, logical drives

  • The boot loader, or the program used to find and load an operating system from one of the drive’s partitions.

Here’s a sampling of error messages, followed by advice about how to deal with them:

Invalid Partition Table: This nasty error message indicates that the partition table is damaged or missing or contains questionable information.

Operating System Not Found: Not a deadly error message, this one might indicate that the partition table has no active partition set: The computer doesn’t know which partition to look at for an operating system.

Missing Operating System: This message most likely implies that the partition table is damaged. The MBR is saying that a bootable partition is available, but not any information about where to find the partition.

Non-System Disk or Disk Error: This old error message often surfaced when a non-bootable floppy disk was left in the drive and the computer tried (by default) to boot from the disk.

When you see one of these first three error messages, the solution is to run the Windows Recovery Console. You can use the FIXBOOT or FIXMBR utilities to address the issues, by repairing the MBR and restoring things to normal.

When a hard drive is damaged beyond repair, it must be replaced. After installing a new disk, be sure to restore your old files from a backup.

The MBR also contains information identifying the disk — a disk signature, which uniquely identifies the disk and may be used by Windows for various and sundry reasons.