A very good piece of information provided by lady_doc77. I would like to add few things. There are basically two type of hard drive crash. one is Logical crash and other is physical crash.
Logical crash occur due to software malfunction, viruses , file/directory deletion or even sabotage. Recovery from Logical crash can be done by using data recovery software such as Stellar Phoenix Windows Data recovery software
which recovers the data even from inaccessible hard drive.
Physical crash occur due to head crash or spindle has stopped spinning. recovery from such cases can only be possible through data recovery services with CLASS 100 Clean Room Lab with a controlled recommended environment for all Read/write Head assembly transplants.