How to Fix the Master Boot Record in Windows
One useful and often necessary thing you can do in the Windows Recovery Console is fix a corrupt or damaged master boot record (MBR). The MBR plays a role in starting your PC and what happens when it’s damaged. Recovery is entirely possible if you can access the Recovery Console and you know which command to type for your version of Windows.
In Windows 7 and Windows Vista, type the following command at the Recovery Console prompt:
Type the command exactly as written: BOOTREC, a space, a forward slash, and then FIXMBR not followed by a period. Press Enter.
In Windows XP, you type the following command to fix the master boot record at the Recovery Console prompt:
Press the Enter key and then press Y and Enter to confirm.
For all versions of Windows, this command works instantly. You see another command prompt displayed. Type exit to quit the command prompt. Restart the PC if it doesn’t restart automatically.
When the computer restarts, whatever problems afflicted the MBR should be gone. For example, if you were removing a boot manager program, it no longer appears when the PC first starts.
No danger is involved in fixing the MBR; if it wasn’t damaged, running the FIXMBR command doesn’t screw anything up (well, unless something else is wrong with the boot drive).