The first thing is to backup your MBR before starting.
http://www.terabyteunlimited.com/utilities.html
MBRWork - Freeware utility to perform some common and
uncommon MBR and disk functions. Provided As-Is.

It can perform the following:

1 - Backup the first track on a hard drive.

2 - Restore the backup file.

3 - Reset the EMBR area to all zeros.

4 - Reset the MBR are to all zeros.

5 - Install standard MBR Code

6 - Set a partition active (avail on the command line too)

7 - Work with multiple hard drives.

---------------------------------------------------

Regards,
Stephen