How to Fix MBR in Window XP, Vista and 7

What is MBR
When the computer system is turned ON the first program that it loads is BIOS (Basic Input Output System).The BIOS also need a memory address from where it can load its Boot Program known as MBR(Master Boot Record) or Master Boot Sector or Boot Sector which starts the further processing .The exact location of this boot record is cylinder 0, head 0 and sector 1 which is the first available space on harddisk. MBR contains all the necessary information for loading the operating system.

Some Error Messages and their Causes:

If your system’s MBR gets corrupted your operating system will not load and this is commonly referred as Window Crash.MBR can become corrupted due to viruses in your operating system or sudden Power OFF.Following are the error messages you will get due to corrupt MBR

• Error in loading operating system
• Missing operating system
• Invalid partition table

You can also get these error messages when you Multiboot your system i.e. installs two operating systems (like Window 7 & LINUX) and uninstall any of them. Now when you try to load the other OS it goes the memory location where the boot loader of uninstalled operating system was present and try to load it. As there is no boot loader of that operating system then it will produce one of the above mentioned error messages.
When a user get these error messages then the first thought comes in his mind is that his windows has been corrupted and he has to reinstall a fresh copy of the operating system.
The thing is that the boot program of the installed OS is present at different memory location on the disk and you have to map the boot loader with the operating system ,not to reinstall the fully OS again.