OK I was upgrading my file server to a quad core, and swap out a few drives. Quad core didn't take, had to go back to the dual core. GA-965P-DS3 doesn't like the Q9400. (updated to the lastest bios as well) After i put the old cpu back in, and plugged in all the drives... One drive wasn't working properly. When I click on it i get the you must format this drive to use it. Checked under disk management and it got detected as a 500gb drive. And I have no 500gb drives hooked up. Turns out one of my 1.5TB drives thinks it's only 500gb!! I went in the bios, and it detects it as a 500gb drive also. I hooked it up via usb to another PC and I get the same thing. I played around with 'testdisk', And after playing around with the geometry settings, things looked hopeful. It found the partition, And gave me the option to write the changes. It says to reboot, But nothing changes. I'm not sure if I'm using it right... or perhaps the disk is just too stuffed. According to testdisk, it detected that the drive had 60,804 cylinders, when my other 1.5tb HDD had 182,401 cylinders. I might be able to use a recovery program, I had a quick look at 'get data back' but I have a feeling it will only try to recover data in the first 3rd of the disk, as it detects the capacity as 500gb also! Has anyone got any ideas of what else I can do? The HDD is a WD15EADS. A quick google search has shown that there's at least one other person to have the same problem.