Is this boot sector fried?

I have a hard drive that the BIOS will not recognize properly. It keeps saying that the drive’s size is 6831, when it should read 20419. It is an EIDE drive. I tried an fdisk, but was told that there were no active partitions, and I tried to reload NT, but was informed that no HD was attached to the system. How could this be, when BIOS was saying that there was (albeit with the incorrect size)? Also, is there a way to fix this? This belongs to the ALRE MO (the guy in charge of fixing the aircraft catapults on my ship), so the data on the drive is very critical. A temporary fix so I could at least back up data would be nice. I’m afraid that the boot sector is fried though. What do you think?