Problems with the master boot record (MBR) of a system may prevent the system from booting. The MBR may be affected by malicious code, become corrupted by disk errors, or be overwritten by other boot loaders when experimenting with multiple operating systems on a host. This recipe describes one method of repairing the MBR for an XP host using the recovery console.
Boot with the XP installation CD.
When prompted, press R to repair a Windows XP installation.
If repairing a host with multiple operating systems, select the appropriate one (XP) from the menu. If you have only one operating system, enter 1 to select it.
Enter the administrator password if prompted.
To fix the MBR, use the following command:
fixmbr
This assumes that your installation is on the C:\ drive. You will be presented with several scary warning lines the reading of which will make you want to say no. Microsoft is exceptionally vague regarding the conditions under which fixmbr can cause problems although they are clear about the consequences (losing all data on the hard drive), so use this at your own risk.
Type y and ENTER to fix the MBR.
Type exit to leave the recovery console and reboot.
In Windows Vista
You can automatically solve most startup problems with the Startup Repair tool. If you prefer a more manual approach, you can use the BootRec.exe tool in the Windows Recovery environment.
First, follow these steps to load the Windows Recovery Environment:
1. Restart the computer from the Windows Vista DVD (the computer must be configured to start from CD/DVD), and start setup.
2. Configure your language preferences.
3. When prompted, click Repair your computer.

4. Startup Repair will automatically detect a problem. When prompted, click Repair and restart, and then restart your computer from the Windows Vista DVD. If Startup Repair does not automatically detect a problem, continue to the next step.
5. When prompted, click Repair Your Computer.
6. Click Command Prompt from the System Recovery Options.

BootRec.exe provides the following command-line paramters:
- /FixMbr. Re-writes the master boot record (MBR) of the system partition to start Windows Vista. This won’t overwrite the existing partition table.
- /FixBoot. Writes a boot sector onto the system partition to start Windows Vista.
- /ScanOs. Scans all disks for Windows Vista installations and displays them to you. Oddly, this didn’t work for me, even on a test system that was starting just fine.
- /RebuildBcd. Scans all disks for Windows Vista installations and prompts you to pick the ones you want to add to the BCD.