Data loss can be broken into two categories Logical and Physical.
Logical : This is the most common type data loss. Logical damage includes accidental file deletion, formatting the drive, computer viruses/worms, and power fluctuations. All of these can corrupt individual files, file tables, and partition information causing a variety of problems from degraded system performance, the computer freezing, all the way up to the system will not start up.
Physical : This is less common, but more likely with older hard drives. Physical includes everything impacting the operation of the hard drive. Drive motor fails to turn, controller card overheating with smoke and a bad smell, ticking – scratching – beeping noises, are all signs of hard drive components physically failing. These could be induced by dropping the drive, defective parts, or just wear from years of operation. The danger with physical failures is damage to the surface of the platters where the data resides. Damage to the platters results in permanent loss of data. Recovering from these types of failures is time and labor intensive requiring a clean room, and exact replacement parts.