How to Repair a Damaged MBR Without a Windows XP CD
The MBR (master boot record) of your computer's hard drive is the location containing all of the important information about the structure of the drive. Accomplish the repair of a broken MBR by utilizing the disk repair utility embedded in the Recovery Console of your operating system. While this would normally require an XP CD to use, you can install the Recovery Console directly from your hard drive.
Click "Start" and "Run."
Type "C:\Windows\i386\winnt32.exe /cmdcons" and press "Enter."
Restart the computer. Select "Recovery Console" as the computer is loading and press "Enter."
Type "fixmbr" and press "Enter."