A hard disk drive (HDD) failure or error is the worst problem a computer user can face, especially when the HDD contains a lot of important information and there is no data backup available. Many external hard drives are made by enclosing standard hard drives in a special enclosure to allow for USB or Firewire interface. However, troubleshooting guidelines are similar. If the hard drive has any kind of errors, you should immediately backup data , since data recovery services are extremely expensive.
How to fix it
There are various types of hard drive problems, some can be easily fixed without much effort, for others you may have to purchase hardware.
1. When you power on the computer, the HDD LED does not light up. There could be a problem with the power and data cable connector on the HDD. Open the computer cover and check whether if the connector is fixed properly .Also check if the power supply to the hard disk is OK ( A multimeter may be needed)
2. When you start the computer, you get an error message, cannot find the hard drive.
a. If you have another working computer available, install the hard drive on the other computer. If the HDD works on the other computer, there could be a problem with the motherboard of your computer .
3. Restart the computer again and check if the HDD is detected by the computer. Sometimes the HDD will work intermittently , before it finally fails. In such cases, take a backup of all important data on some other media like CDR or flash drives . Install a new hard drive on your computer, since new drives cost less than US$100.
Alternately, you can transfer data from your old HDD to new HDD by configuring the new HDD as master and old drive as slave.
4. Some people suggest sealing a drive in a bag and keeping it in a freezer overnight. The PCB side should not be exposed to air to avoid condensation. Cooling the HDD will shrink components on the drive and it may start working. The hard drive may work only for a short time, and stop working after the hard drive heats up.
5. Try to find out the likely cause of drive failure. Before a drive failure due to mechanical problems, the drive will make noises and cause read/write errors. Electronics errors are sudden but can be fixed by replacing the circuit board on the drive. The circuit board is usually not sold by manufacturers but available on auction websites like eBay
6. Sometimes, the error is due to damage to the file structure on the drive. In such cases, reformat the drive.