I offer this and anyone wanting to add or correct can do so. Understand its offered as an incomplete list, thought I feel it covers typical failures. -----Willy
External drive failures of HD or flash/thumb drives
3) improper dismount(corruption)
4) ESD(static) damage
5) port or drive contacts
6) exposure to elements
7) USB port voltage/ampage low/high
80 OS, USB issues
Failure causes can be attributed to many things but the above should touch on what maybe your reason for failure. It is but no means emcompasses all failures but does seem to be most common. The following will try to explain each failure and its cause.
1) Improper handling can introduce ESD or intolerance even though robust devices, they shouldn't be moved during use. Some ext. HD drives are so quite you thought its working, but look for telltale LED or being "ON".
2) You drop it more than likly it won't work, though you could get by for awhile or simply luck out until next time. Beware of kids and pets.
3) Once a drive is done its task and want to remove it, go through the dismount procedure. Doing so reduces occurance or corruption or data loss. usually the wording used is "eject".
4) ESD damage from static is highly possible. Those users that mount a ext. drive are the contact point to discharge. So, beware of ESD build-up as 5-12V is used to run a drive, ESD voltage far exceeds that.
5) Dirty contacts at port or cradle can cause "non-contact" or less than desired full contact. Further, some cradles(docks) are nothing more than simple wieght-bearing contacts. If you use a cordless phones, you know what simple cradle is.
6) Exposure to elements or anything other than typical desktop or PC enviroment is asking for trouble. While flash/thunb drives tend to be robust, they do fail sooner or later. I exclude the family pet.
While success stories abound of washing machines, auto run-overs, left on dashboard, etc., back-up ASAP if this occurs.
7) A limited voltage/ampage is availble through USB ports. Some makers address this with a USB dongle to help, use it. Use the rear USB ports for best operation when available. Prolonged and repeated prolonged usage can force the USB port to fail of itself as quality of the motherboard is tested by "solder lands" separation or componet failure. This is more pronounced in laptops, which maybe using several USB devices at once or attached. The PSU starts to waver in stable
outputs, causing damage. This can be related to system heat stress/build-up.
OS updates, chipset issues, the device driver/software may become corrupted or be improperly reset as time marches on. Try a restore point to return before the problem arose. Check system poporteries, etc. to see if the cause. However, don't jump immediately into a software issue as cause, because if msihandled will cause issues of its own. Just thread carefully in this area.