Restaurar mbr windows

1. Boot your computer to the Windows 7 DVD (or to a "Repair CD"). At this screen choose to install now.

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2. Select your language and click next.

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3. Click the button for "Use recovery tools".

4. Then select "Command Prompt".

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5. When open, the command prompt will look like this:

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6. The command we will use, bootsect.exe, is in a folder (named boot) on the DVD.

We need to know what drive letter has been assigned the DVD drive to access the folder.

Code:

Type: diskpart
and press Enter
 
Type: select disk 0 (zero)
and press Enter
 
type: list volume
and press Enter

In this screen shot, the 7 DVD is letter: G

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7. Use your DVD drive letter and

Code:

Type: exit
and press Enter
 
to close Diskpart
 
Type: G: (use the letter of your DVD drive)
and press Enter
 
Type: cd boot
and press Enter
 
Type: dir
and press Enter

to verify that bootcect.exe is there (if you really need to)

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8. To restore the "bootsector code":

Code:

TYPE: bootsect /nt60 SYS /mbr
and press Enter

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NOTE: If this method fails to restore the MBR, you can try the bootrec command as it is also a tool for repairing the MBR.

9. When completed successfully,

Code:

Type: exit
and press Enter

This will close the command prompt window.

10. Now select Shut Down or Restart

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11. Then you can reboot your computer into Windows.
fonte : source :
http://www.sevenforums.com/tutorials/20864-mbr-restore-windows-7-master-boot-record.html