Master Boot Record (MBR) Read Only?

Hi, I have a Latitute D400. My MBR seems to be read only. I tried fixmbr, fdisk /mbr and delpart, all failed to save the changes I made to the MBR. The error message I got when I use delpart is "Unable to write master boot record on drive 80H". And the error message I got when I use fdisk /mbr is "master boot code has not been updated". Is there something that is preventing me from writing to my MBR. I have upgraded my BIOS to the latest 0.8v to no avail. There is no indication in the BIOS that specifies that a virus protection is turn on. Please help.