What you should not do:
1. Switch the computer on and off for several times while it is clear that the harddisk does not work. In case of a malfunction of the harddisk, the magnetic disk surface, and thus the stored information may be further corrupted.
2. Put the harddisk in the fridge or roast it. Although a number of forums will encourage to do so. Even if the malfunction is due to overheating of the components, the strong cooling can only, if at all, activate the harddisk for a few seconds. This time is insufficient for a data recovery. There are also cases where the hard drive works again momentarily after some rest (not within the refrigerator). But these cases are extremely rare.
3. Unscrew the hermetic case.
Even if the hard drive no longer starts, it is still far from clear that the engine is broken or locked. Quite often it is the controller that, due to an error, gives no signal to start the engine. Sometimes the heads suck to the magnetic surface outside the parking zone. This results in scratches if the wheels are turned forcibly. Quite irrespective of the fact that thereby dust gets inside the harddisk.
4. Replace the controller, if one is not sure that this is really the problem and that the harddisk type allows to do so.
In doing so, one risks to lose both the data as well as the controller. Due to achieve the large data densitiy of modern hard drives, the controller is set individually for each harddisk and therefore cannot be replaced with an 'identical' PCB. Attempts to do this anyway will only result in clicking of the hard disk. Sometimes even the exchanged controller will be destroyed.
5. Solder elements of the controller, if you are not sure that this is the reason for the malfunction.
6. Run programms such as CHKDISK, SCANDISK, Partition Magic etc. ,
if one is not sure that they can really fix the error. If the hard disk has malfunctions or surface damages (Bad Blocks), the programs can restructure the still existing data in a way that the correlations are not found anymore.
7. The tips from the Internet should be applied with great caution since they have unfortunately not always been written by specialists. The solutions for hardware damages are usually very strong related to the specific model of the harddrive. One should be careful in forums that advice for hardware repair without designating the exact model type.
If the drive is not recognized by the BIOS and makes unusual noises such as tic tac sound, the disk is defective. You should not plug it to another computer, not in an external casing, not try it on Linux, etc.
Failure to comply these precautions can aggravate the data recovery process or even make it impossible.