Problems:
External USB and Firewire hard disks basically consist of a case containing a standard IDE hard disk with a USB-to-IDE or Firewire-to-IDE interface adaptor. Thus, these units are prone to all the usual problems relating to IDE hard drives plus some others that the external case and interface may bring. The most common additional problem we have noticed with these drives is their tendancy to overheat. This is due to inadequate ventilation on the external case. Early external hard drives didn't contain any ventilation at all, modern devices often contain a small fan inside the actual case to combat temperature build up.

Symptoms:
The drive will suddenly die and not be recognised by the BIOS, or the computer will appear to start running slowly and noises from the external hard disk may be heard.

Cause:
Failure of these units is often (but not always) heat related. They are also more likely to suffer impact damage as it's far easier for these drives to fall out of bags or off of tables etc.

Do Not:
Under no circumstances should you continue to use the device as you may cause further damage to the unit. Also, you should not allow the system to run a repair utility on the drive (such as Scandisk / Chkdsk / Norton etc) - this can often render recoverable data unrecoverable