MBR (Master Boot Record), also known as Master Boot Sector, is the master boot record of a hard disk. MBR consists of three parts, i.e. Boot Loader, Partition Table and Magic Number. Boot loader is a program that loads an operating system when a computer is turned on. Partition table records partition information on local disks. Magic number(0xAA55/0x55AA) marks the device as a valid bootable media. An invalid magic number indicates a corrupted or missing MBR. Master Boot Sector contains 512 bytes in total, of which the boot loader takes up 446 bytes, partition table 64 bytes, and magic number 2 bytes.
In some cases, the code segment of MBR may be damaged by virus attack, improper operations, and unknown reasons. The phenomenon is that your computer cannot enter the operating system and keeps black screen, or cursor blinking, saying “Operating System not found”. If you confirm there is no physical fault in hard disk, you should consider MBR damage as the chief culprit.
Since your computer cannot get into system, you need to fix MBR by virtue of bootable disks. Try using the following methods to repair master boot record.
1. Use “fixmbr” command
Use any DOS startup disk to activate MSDOS prompt, input command “fdisk /mbr”.
Install toolkit and add “fixmbr command line” tool. Use Win XP boot disk to boot your computer and execute “fixmbr \Device\HardDiskX”. (Depending on your disk layout, X could be 0, 1,2, 3…)
Same with Windows XP, but the command is “bootrec /fixmbr”.
2. Use partition software
Another feasible method is by using third-party software to fix MBR effortlessly. There is lots of partition software in the market that can achieve this goal, and MiniTool Partition Wizard Bootable edition is among the most reliable ones.
MiniTool Partition Wizard Bootable edition is an all-in-one bootable partition manager which can meet all your demands for disk/partition management under bootable mode when operating system fails to boot.
Today Windows still holds a huge market share, and the risk of MBR damage is relatively high. To explain how to rebuild MBR with MiniTool Partition Wizard Bootable CD, let’s take the most classic operating system – Windows 7 for example.
Step 1. Download the iso file of MiniTool Partition Wizard Bootable DC.
Step 2. Burn the iso file to a USB flash drive or CD/DVD Disc.
Note: If you have no idea of how to create a bootable media, this article may help you a lot: How to Build Free Bootable Partition Manager with Pwfree91.iso?
Step 3. Set your computer to boot from this bootable media.
Connect the USB drive (or CD/DVD disc) with your computer, and then boot your computer into BIOS. Now set to boot from the bootable device and save your change.
Note: If you are using a CD/DVD disc, you need to boot your computer firstly. Otherwise, you cannot place the disc into CD-ROM. After that, you can set the computer to boot from CD-ROM Drive.
When you see the following picture, just follow the default settings.
Step 4. Fix MBR in Windows 7
Now MiniTool Partition Wizard Professional is already there waiting for your operation. Select the disk that contains operating system and choose “Rebuild MBR”. Last but not least, press “Apply” to execute the operation.
Step 5. Now, you need to set your computer to boot from system disk. After that, Windows 7 will startup normally.
Now you know how to fix MBR in Windows 7. Next time when your computer says “Operating System not found”, you won’t be anxious like an ant on a hot pan.