I had a "click of death" with my hard drive after it fell on the floor. It was neither detected nor spinning when I plugged it in. I tried to switch the PCBs since I had exactly the same PCB from another HDD. It didn't help. I also tried to freeze it which also didn't work. Then I just tried the "shock" method. After few tries I heard no click anymore after plugging and the drive was spinning. Now the thing is that though it is spinning and clicks no more, it is still not detected by the OS. The "fdisk -l" command shows nothing. Any ideas? Thx.
Now is a great time to remember to back up all your data ;) That's how most people (myself included) learn to do backups - after one or more of these - usually just before a deadline.
I'm not sure about current disk design, but the way I think it works is that the heads fly a very tiny distance above the platters - microns - where even a tiny dust particle can do serious damage. So, unless you have access to a clean room, opening the disk will almost guarantee that your data is permanently lost.
If your data is critical or expensive to recreate, you can send the drive to a data recovery service (not cheap!). They do have clean rooms and know a lot about digging in byte by byte to get things back.