This example shows the status a Western Digital 250 GB external hard disk (used in "MyBook" enclosure).
absolutely nothing: hard disk is working correctly
all files and folders are properly accessible
hardware self tests and Surface test functions from Disk menu shows no problems with the hard disk in general or the hard disk surface
Initially, the hard disk health reported is 100 %.
The hard disk status is PERFECT. Problematic or weak sectors were not found and there are no spin up or data transfer errors.
Power on time: 176 days, estimated remaining lifetime: more than 1000 days
However, in the main window the temperature level is immediately displayed with red color. Opening the "Temperature" page shows even more details:
The temperature level is far above the highest acceptable 50 Celsius (55 Celsius for some hard disk models or maybe 60 Celsius for some very-specific models, for example industry SAS hard disks). This high temperature can seriously damage both the mechanical and electronical parts of the hard disk.
Note that the "Average temperature" reported is fair because the hard disk just powered on and the temperature just increased to 67 Celsius. Using the hard disk for just copying/moving some files would quickly increase the "Average temperature" to 60+ Celsius degrees.
This is why the "Temperature" page shows the following notice:
Current temperature is too high.
After some days of usage on this high temperature, the drive become inaccessible. It is automatically disconnected from the system during a high load with the Windows message "Delayed write failed". Next time the hard disk was not properly identified by the computer. Hard Disk Sentinel even shows "WD 2500JS External" as model ID and the reported disk capacity is incorrect (0 bytes).
As the administrative area of the hard disk become damaged or in-accessible, the hard disk cannot properly identify itself and access any sectors from the data area. In this case, invalid model ID (for example: WDC ROM MODEL-MAMMOTH-- , WDC ROM MODEL-HAWK----- etc.) reported. Also the serial number seems invalid (WDC-ROM SN# XYZ----) and usually the capacity is not reported properly (the hard disk drive appears as 0 bytes or 8 GBytes capacity).
In this case, the hard disk drive cannot be repaired by software, only data recovery companies may help. Its cost varies in different countries (data recovery can be $2000-5000 USD per hard disk drive), but it is better to avoid this situation.
It is always recommended to verify the hard disk temperature levels.
Verify the accuracy of the temperature sensor and adjust the reported value if required (see Help -> Temperature calibration section for details).
Use passive or active cooling device(s) to keep the drive in green or yellow temperature range (even during intensive disk operations). Even positioning a simple fan over an external hard disk (to cool down the external hard disk case) may reduce the hard disk temperature with 5-10 Celsius degrees.
Carefully use external hard disk enclosures (especially plastic ones) as they may prevent cooling of the hard disk(s) inside.