I’ve run into a problem several times where I get an unloadable boot sector error.  Often you will have to repair the Windows Boot sector, or do some recovery work with the MBR.  The easy way to do this is to use the Windows Vista Bootrec.exe tool in the Windows Recovery Environment (Windows RE) to troubleshoot and repair Windows Vista.  Here is a step by step guide.
Using the built-in Vista tools you can repair;
• A master boot record (MBR)

• A boot sector

• A Boot Configuration Data (BCD) store

To run the Bootrec.exe tool, you must start Windows RE. This is a similar process to the old Windows XP Reconvery Console.  To launch Windows RE, follow these steps:

1. Put your Windows Vista installation disc in the disc drive, and then start the computer.

2. Press a key when you are prompted.

3. Select a language, a time, a currency, a keyboard or an input method, and then click Next.

4. Click Repair your computer.

5. Click the operating system that you want to repair, and then click Next.

6. In the System Recovery Options dialog box, click Command Prompt.

7. Type “Bootrec.exe”, (without the quotes) and then press ENTER.

The Bootrec.exe tool supports the following options. Use the option that is appropriate for your situation.

/FixMbr

The /FixMbr option writes a Windows Vista-compatible MBR to the system partition. This option does not overwrite the existing partition table. Use this option when you must resolve MBR corruption issues, or when you have to remove non-standard code from the MBR.

/FixBoot

The /FixBoot option writes a new boot sector to the system partition by using a boot sector that is compatible with Windows Vista. Use this option if one of the following conditions is true.

· The boot sector has been replaced with a non-standard Windows Vista boot sector.

• The boot sector is damaged.

• An earlier Windows operating system has been installed after Windows Vista was installed. In this scenario, the computer starts by using Windows NT Loader (NTLDR) instead of Windows Boot Manager (Bootmgr.exe).

/ScanOs

The /ScanOs option scans all disks for installations that are compatible with Windows Vista. Additionally, this option displays the entries that are currently not in the BCD store. Use this option when there are Windows Vista installations that the Boot Manager menu does not list.

/RebuildBcd

The /RebuildBcd option scans all disks for installations that are compatible with Windows Vista. Additionally, this option lets you select the installations that you want to add to the BCD store. Use this option when you must completely rebuild the BCD.

Note: If rebuilding the BCD does not resolve the startup issue, you can export and delete the BCD, and then run this option again. By doing this, you make sure that the BCD is completely rebuilt. To do this, type the following commands at the Windows RE command prompt:

• bcdedit /export C:BCD_Backup

• c:

• cd boot

• attrib bcd -s -h -r

• ren c:bootbcd bcd.old

• bootrec /RebuildBcd

Tags | Microsoft, Windows Vista