Lembro-me de corrigir meu MBR com um CD do Windows XP que permite inicializar com o Prompt de Comando.
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.
Fonte: Corrigir registro de MBR usando o WinXP