Thanks for the detailed advice. I've tried a different IDE usb cable; both cables allow the laptop to read the type of HD in the enclosure ( WDC WD 40 OBB 00DEA0 USB device), and the Hitachi DK25EA - 40 in the laptop shows as well. 
System Properties shows two HDs, the ones above.
 
 I don't think the jumpers have been altered since it was last used.

Am I right in assuming this means all connections are OK, and the external HD in the enclosure is at least 'alive' to the extent its HD identity can be read? To Test this idea, I put another HD in the enclosure and hooked it up to the laptop - and My Computer showed it as 'drive E'.
 
It would appear to me this indicates the Hard Drive WDC WD40 is somehow faulty, despite its vibrating when powered up, and being read as present. 
 
Is there any way of getting at its contents?
--- On Sun, 26/7/09, Hugh Vandervoort <[log in to unmask]> wrote:


From: Hugh Vandervoort <[log in to unmask]>
Subject: Re: [PCBUILD] USB encosur HDl
To: [log in to unmask]
Date: Sunday, 26 July, 2009, 7:08 AM


Can you see it in Disk Management? Has it been dropped or damaged in
any way? Have you disconnected it without using the "Safely Remove"
option?
There are several possible points of failure, including the drive
case, the cable and the drive itself.
It's also possible the connection between the case and the drive is
loose. I believe this is a SATA drive, and some of those cables are
not particularly secure.
If you can't see it in disk management, remove it from the case and
check the internal connector, or try another case or a USB adapter.



On Sat, Jul 25, 2009 at 7:09 PM, Ronald Smith<[log in to unmask]> wrote:
> Hello
>
> I have a usb hard drive for backup (WDC WD40 0BB-00DEA0 USB Device) which comes on when plugged in (blue light, vibrations), but does not show up in My Computer, despite appearing  in Device Manager and showing up as working and having drivers.
>
> This HD in its enclosure( Pluscom 3.5 IDE to USB 2.0) did show previously and was used to backup the C drive. But now it is absent from  My Computer in all three computers on which it has been tested.
>
> Why is it no longer recognized, and how can I restore it to use?

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