There are 3 main reasons a hard drive will not spin up. Bad fluid bearing, bad motor, but the most common problem is the printed circuit board (PCB) may become damaged.
The liquid bearing and motor failures are internal problems that require the hard drive be completely taken apart and rebuilt with special tools by a well trained data recovery technician. This is a very challenging recovery for even top professionals. Never open your hard drive yourself as it will be contaminated by dust particles, static electricity and humidity. Data recovery specialists use a class 100 clean room to protect the platters from these pollutants.
PCB failures are among the most frequent problems. A common mistake that people make is that they simply try swapping the bad board with another board from a new and seemingly identical hard drive. We have heard of this working a very small percentage of the time, possibly as much as 1% however we are very skeptical about those claims. If the ROM chip hasn’t been removed from the damaged PCB and swapped to the new donor PCB it can make the drive start clicking. In short the clicking sound is the heads malfunctioning; instead of reading the media normally they just bounce back and forth making the “click of death”. When the heads malfunction like that it causes a vibration and because the heads are so close to the platters they make contact with each other. In the business we call that a head slap. It causes permanent data loss that cannot be undone. Swapping the ROM chip should only be left to the data recovery professional. Attempting to remove and replace the ROM chip with the wrong soldering equipment and improper technique will result in the destruction of the chip and complete data loss.