Like every component and hardware, hard disk drives also have their life and limitations and they also go into failure and crash. Although 
they go into failure spontaneously some times too, there are still some signs that may help in getting alarmed before the disk drive crashes so that you can backup the data on it before hand.
Some of the signs and indications that the hard disk drive shows before going into failure or crash are as follow:
Occasional Clicking Sound
Commonly before the hard drive fails, it starts giving clicking sound. This sound signifies that there is malfunction in one of the internal components of the hard disk drive (mostly actuator arm) and its freely swinging around and touching other components, resulting in that clicking sound from your hard disk drive. When the actuator arm is broken, the hard disk might work normally though, but this will cause the user to overlook it and the fault may lead to permanent data loss and malfunction of the hard disk drive.
If you encounter this situation when your computer starts giving the clicking sound, immediately backup your important data and consult some technician or data recovery specialist if needed.
Constant Clicking Sound:
Constant clicking sound comes when the actuator arm is broken in the hard disk drive, and its swinging freely inside it, touching the internal components and the hard disk is not performing read/write function. You might need to consult a data recovery expert in that situation to get your data recovered!
No Power / Spinning
One of the form of failure of the hard disk drives is that they fail to power up and no power light (if any on mother board or else where)) or spin sound is there to confirm the power function of the hard disk drive, even though the power is intact properly and the same setup and cable works fine for other hard disk drives. If you get in such situation, then possibly its gone now! You might need to consult the expert to get your data back from it and if this could be fixed in some condition too.