I think I have a similar problem with the same disk model. I had the HDD in a USB external housing, by mistake, connect the power source of the labtop to the USB external housing, giving over-voltage and amperage.
I bought a hard disk of the same model to take the PCB and put it into the damaged disc. first thing I notice is that the PCBs are not exactly alike.
before changing the PCB, connect the new Harddisk to the PC, the PC recognizes the drive and mount the disk driver but never appears on my pc, I try this is another PC with the same result. this makes me think that the disc is not quite right.
I take the new PCB and place it in the old HDD. then, when I turn on the PC, it shows an error message when loading the disk, before load the operating system.
I was so excited about it, not notice that the PBC has a different number after two days, even when the same disc, I guess that this should be the difference in the PBC components.
Here the HardDisk Damaged Data
HITACHI MODEL: HDT721010SLA360
P/N: 0A38016
PCB: 0A29989
http://img585.imageshack.us/img585/7342/img9128d.jpghttp://img228.imageshack.us/img228/4548/img91472.jpgHere the new HardDisk Data
HITACHI MODEL: HDT721010SLA360
P/N: 0A38016
PCB: 0A29987
http://img407.imageshack.us/img407/5228/img91272.jpgother data, I put the new HardDisk on a NAS (D-link Share center 320), in order to see if the disc works. during formatting five error messages are showed. I press "skip and continue". finally finished formatting. Then I tried copying and playing files on the disk and apparently works well, also made Scandisck and SMART Test with the NAS, both result ok.
Returning to the case, after reading this post. try to measure with a tester PCB components damaged. place the tester to measure conductivity. conductivity observed in the components shown in red. these same components in the new PCB show do not conductivity.
http://imageshack.us/photo/my-images/68 ... amage.jpg/Please tell me what I can do. I do not know electronica, but every time there is a challenge trying to learn as much as possible. I am a chemist and amateur photographers. my best approximation to the electronics was at the university and when I was a child I had an electronic game called "150 in 1" made by RadioShack.

I'll go read the post that recommended by fzabkar.
Two questions. I can do with the damaged hard drive?
What happens to new HardDisk?
Best regards.