In Windows Vista and later versions of Windows operating systems, the booting process is controlled by the bootmgr file. This file targets the BCD (Boot Configuration Data) store to get the list of operating systems and load the most suitable one. Also, this BCD store stores the information of the boot time configuration data and its well being is very significant for the boot precess. Therefore, when this file gets corrupt the system is unable to start as the active partition cannot be located. You can utilize in-house Windows tools like bootrec.exe to recover Windows partition. If that does not help, then I would suggest to use a third-party partition recovery software to do the needful.

Talking of similar instances, consider you are trying to start your Windows Vista system but fail to do so at the booting phase.

Cause:
These situations can appear when either of the following boot components of Windows Vista system are corrupt:
Master boot record (MBR)
A boot sector
A Boot Configuration Data (BCD) store

Resolution:
To rectify this problem, you should try out the following steps:
Insert the Windows Vista installation DVD in the DVD-ROM drive and restart the computer.
Press any key when the ‘Press any key to start’ prompt is displayed.
Select the following entries:
Language
Date and time
Currency
Keyboard or input method
Click Next, when done.
Click the ‘Repair your computer’ button.
Select the operating system that is to be repaired.
Click Next.
Click ‘Command Prompt’ in the System Recovery Option dialog box. The Command Prompt is displayed.
In the Command Prompt, enter ‘Bootrec.exe’ and press the Enter key.
Here, you can use the following options:
/FixMbr
/FixBoot
/ScanOs
/RebuildBcd

Using the aforementioned options of the Bootrec.exe tool, you will be able to repair the booting components of Windows Vista. Having said that, there may be few instances when the problem does not get solved using these options. In such cases, partition recovery becomes very important otherwise all your data could be  lost forever. For such uses, a good partition recovery software comes to your rescue as it can easily recover partitions corrupted because of any reason.

Of all the partition recovery tools, Stellar Phoenix Windows Data Recovery is one of the best partition recovery software around. Compatible with Windows 7, Vista, Server 2003, XP, and 2000, this Windows partition recovery software supports recovery from FAT, NTFS, or exFAT file systems. Also, this email recovery software is able to restore more than 185 file types from various kinds of storage media.