I've read that you can't use FDISK/MBR to repair the MBR if the system is using a special disk overlay program that reside in the boot sector.
What is a disk overlay program?

See this
http://www.pcguide.com/ref/hdd/bios/overDDO-c.html

I've been using this for quite some time and have never had any problems with it.

Thanks Sylvander, I suspected it to be something like EZ Drive. I wasn't familiar with the term overlay program in connection to the disk drive.