MBR is short for Master Boot Record, it is the first part of your hard drive where BIOS looks for an operating system on your PC and if the MBR on your system is corrupted then your system will not load the operating system. When this problem occurs, your system shows an error like these:

Error loading operating system
Missing Operating System
Invalid partition table

If your system has MBR problem, follow these steps to fix MBR problem

1. Insert the Windows XP disk into your CD drive
2. Restart your computer
3. Press any key when “Press any key to boot from CD Rom” appears
4. Once Windows XP Setup loads, you will see an option “To repair your Windows XP installation using Recovery Console, press R”, select it and press Enter
5. When the system enters Recovery Console and loads, you must enter a number that matches your Windows installation. This number is usually 1
6. After typing the number, press Enter
7. Type the administrative password and press Enter
8. Now type the fixmbr command at the command prompt, this command will replace your old MBR with a new MBR and help your system to boot properly.

You can only use this command on a system that has an operating system installed. If you have installed multiple operating systems on your computer, this command will create a mess for you.

Sometimes MBR error also occurs due to corrupt Windows registry and it can be fixed simply by repairing the registry. You can use some system utility that can clean Windows registry, defrag registry, clean system junk and optimize computer services.

Such software can help you avoid such errors in the future.