Unable to mount two external hard drives

I’ve been using a WD My Book external hard drive for two years and it ran perfectly until a couple of days ago when the icon disappeared from my desktop. (I’d just pulled out the cable without exiting properly, but I’d done that countless times previously.) I’m on OS 10.5.8

It still works (i.e. it lights up and purrs when plugged in) and I’ve tried to get into it on my desk computer using two different cables in three different USB ports. I’ve also tried with and without a Firewire cable. I have a Macbook as well, so I also tried on that to see whether it was my computer or the device. 

The hard drive is visible Disk Utility and System Profile, but I can’t manually remount it in Disk Utility, even though I’ve repaired it many times since the crash and nothing seems to be wrong. 

Having looked on various forums, I’ve tried doing a factory reset (although I’m not sure I really got it right) and a PRAM reset, although I only got the startup sound once.

I have another more recent My Book (Studio 2To), which I used once and did a full back up and haven’t been able to access again since then…

Does anyone have any other ideas? 

Many thanks

Try unmount and disconnect the drive, shut down the computer.

Re-start the computer, then plug in the drive.

Will this work? If not, unplug the drive.

Try update all Mac software, re-start the computer.

After that plug in the drive,

If it is still not work,

unplug the drive,

uninstall all of WD software,

Re-start the computer and plug the drive in, will it work?

If yes, you are done.

None of any of that has worked…