MBR is short for master boot record. MBR consists of three parts, i.e. Boot Loader, Partition Table and Magic Number. Boot loader is responsible for loading OS when a computer is on. Partition table records partition information on local disks. Magic number marks the device as a valid bootable media. An invalid magic number indicates a corrupted or missing MBR. If the first part of MBR is damaged, you won’t be able to boot into Windows.
But in many case, when you boot up computer, Windows report the following message:
1.”Error loading operating system¬_”
2.”Operating System not found_” or “Operating System missing_”
3.”Invalid partition table_”
4.”Reboot and Select proper Boot device or Insert Boot Media in selected Boot device and press a key_”
In these situations, you have to find a way to fix MBR in Windows 8.
Boot from Windows 8 installation media, at the welcome page, select Repair your computer. Then choose ” Troubleshoot > Advanced options > Command Prompt”.
When the Command Prompt loads, type the following commands in order and press Enter after each command:
Finally, Remove the DVD from the disk tray, type exit and hit “Enter”. Restart your computer and check if your Windows 8/8.1 can boot now.
If you do not have Windows 8 installation Media and you feel it difficult to operate commands, you can turn to MiniTool Partition Wizard Pro to get help. It enables to create a bootable media which can be used to boot your computer without OS. Please follow the guides to do the preparatory jobs:
How to Build Boot CD/DVD Discs and Boot Flash Drive with Bootable Media Builder?
How to Boot from Burned MiniTool Bootable CD/DVD Discs or USB Flash Drive?
When you see the main interface of MiniTool Partition Wizard, you can select the system disk and choose “Rebuild MBR” from the action panel. Or you can right click the system disk and choose Rebuild MBR from the shortcut menu.
Then click Apply on the menu bar.
Boot your computer from the local disk again and check whether the operating system is fixed.
Tip: if repair MBR Windows 8 does not help, you may consider reinstall Windows operating system. In this case, you can also use MiniTool Partition Wizard bootable media to back up the whole disk before you make a clean reinstall. For more information, read our post How to Backup Computer to External Hard Drive in Windows 10/8/7.