Except if the Spindle Motor itself fails, any other reason is not a big problem.

It is difficult if the Spindle Motor fails because un-assembly of the main pole.

Turn on the power and put your hand on top of the hard disk`s cover and check if the motor is running. You must be sure of the difference of ones that do not spin and ones that spins about 3 times and stops for exact checking.

Not activating board can be another reason.(Be careful when exchange of main board from SCSI especially Seagate Co. products or high memory products. It may be impossible to recover if not the same board of purchase.)

When there is a problem with the HDA it is best to not to do further operations.