There are several different types of failure of a hard disk.
"Crashed" refers to one particularly nasty type of failure where one of the disk heads hits the disk surface causing scarring on the disk surface and normally destruction of the disk head. Debris from the crashed head can contaminate other platter surfaces and cause other heads in the drive to crash. The particular platter (disc) that is damaged is normally no longer accessible particularly on the part of the disk where the scar is. Other platters in the drive should still work providing they have not suffered secondary damage, although any files that included parts of the file on the damaged platter may be considered lost. Large files are more likely to suffer missing segments from such a failure. Head crash failures are often accompanied by screeching noises from the drive as the head and disk come into contact.
On older drives, the heads are allowed to land on an unused part of the disk when the drive stops. Later drives have a parking area for the heads that lifts the heads clear of the disk surface. On drives that land the heads on the disk and have had a large number of start-stop cycles, the static friction between the heads and the platters increases as the heads polish the discs when they land. Eventually, the static friction may be too much for the motor to spin the disk when power is applied. Sometimes rotating the drive sharply in the plain of the disk so that the disk moves with respect to the heads is enough to allow the drive to work for a few more hours.
If the motor is not spinning the disk, then this can be an electronics failure. In this situation, replacing the electronics board with the board from an identical drive can allow the disk to be copied.
Electronics failures can also prevent the drive from reading its data even if the motor is working. Again, replacing the electronics boards will often allow the data to be recovered.
Finally, a major corruption of the disks file system can appear as though the disk drive has failed. Specialist recovery software may be able to recover lost files. A scandisk may not be able to repair the file system after a major corruption.
Recovery procedures that involve opening the sealed chamber where the platters and the heads operate can cost hundreds of dollars, and if the platters' surfaces are damaged, the results are not guaranteed.
Recovery procedures that do not require the sealed chamber to be opened will generally be much cheaper. There is still no guarantee of complete success.