If your hard drive encounters a serious error (perhaps a failed operating system install, corruption or a virus) then you may get an “Error Loading Operating System” message on boot.

This often means that you have a corrupt Master Boot Record (MBR) which can be fixed with the Vista repair tool. This should be one of the first things done to resolve the above error message, as performing a format and reinstall will cause a loss of data.

First, insert the Vista DVD into the computer and restart it (to start the boot process). You will be asked to press any key to boot from the DVD

Then, fill in the language and location options and click Next

Now, click Repair your Computer in Left Hand Corner.

Then, select your Vista partition and click Next

Select Command Prompt from the system recovery options window

Once you are at the command prompt, run the following commands

Bootrec.exe /fixMBR
Bootrec.exe /fixBoot

The first command fixes the Master Boot Record, and the second fixes the Boot Sector (just in case it is also damaged).

You can now close the command prompt, remove the Vista DVD and click Restart. This should reload Windows with a repaired MBR

You may have noticed there was a “startup repair” option in the Vista boot application. This may also be able to fix your startup problems, but this slightly longer method will fix MBR problems.