I have a 2.5" HDD housed in an aluminum USB external casing. Yesterday I had a freak accident of dropping it on the solid concrete ground.

At night, I tried plugging it into the USB port of a computer and I can hear it clicking but cannot spin up or read.

I was fearing for the worst already, that all my data on the HDD maybe gone.

I have had a similar situation before with a HDD-based MP3 player a few years back where I also dropped it also. It may have been the read head of the HDD got disloged or something, because I keep on banging and tapping the MP3 player and perhaps bang the read head back in place and the MP3 player was able to start up again.

So following the same method. I tried banging this portable HDD. I was getting worried after many bangs and taps and it's still doesn't work until one final bang ... "whewwwwwww" ... the motor spins again, and I was able see the USB drive pop up in Windows.

Okay. Now my question is, since I did drop the portable HDD and the read head may have been disloged, should I worry about the reliability of the read head may randomly become disloged again with "normal" use?

Or should assume that the HDD failure is imminent in the near future and I should not use this HDD at all and just go buy a new one to replace it?

NOTE: Regarding that HDD-based MP3 player, after the drop and banged back in place, it still works to this day, although I don't use it that often nowadays.

Well, reading about all the banging and dropping made me wince. The fact that banging it around "fixed" it should immediately give you some concern. Personally, I would not save anything of importance on it if the HDD is damaged, because it could fail at any moment.

What you are now going to want to pay attention to is that clicking noise followed by a reboot. That will mean that you have a physical surface error on the disc, which is not repairable. I had it happen to me before and it only gets worse.

This may not be too much help to you, but it's my thoughts on your scenario. If you can afford to simply replace it, that might be the best thing.