External hard drive not recognised

[Roobarb]

I've tried Googling this problem but the answers are all too technical so thought I'd ask here for some straightforward information. 

I have a large capacity external hard drive which was successfully used for some time at my IP address by my computer (which I'll call computer A) and another, now defunct computer (which is not now relevant to the question).

Some time later the hard drive was successfully used at a different IP address in another computer (computer B), although it only favoured one port in that computer. It was used numerous times in that computer and a great deal of data added.

After some time the hard drive was returned to me and I used it in computer A to transfer a number of files to a new hard drive. When the (original) hard drive was then used again in computer B, the computer would not recognise it, regardless of which port was used. None of the files can be opened on computer B.

Can anyone please tell me in simple terms why this might have happened and what I can do so that the files can be opened on computer B?

[jim1]

Put it back in computer A & use  "safely remove hardware" to shut it down.

[Roobarb]

Okay -so would that mean it couldn't be used in computer A again? Or could it be used if computer B user had been more conscientious about doing these things properly? 

[groom]

I think, from my limited knowledge, that it could mean that if you just pulled it out and didn't go through the correct procedures when you removed it from computer A, that when you connect it to Computer B, it is still looking for A and doesn't recognise B. 

[Roobarb]

Thank you so much jim1 and groom, I'll give that a try.  I promise I'll do it properly in future.     

[jim1]

so would that mean it couldn't be used in computer A again?

Once it's shut down correctly & you get the "safe to remove" message you can use it anywhere.

[Roobarb]

Thanks jim1, such a simple solution.  My own fault but I panicked when I read some suggested solutions on the internet, talk of partitioning and all sorts of technical stuff. I should have remembered that Rootschatters have sorted so many problems for me in the past.

Thanks again. 

[jim1]

It's a good idea to use this method with all storage media eg. memory sticks.

[Roobarb]

I'll take your advice jim1, than you.