External Hard Drive Won't Mount on Desktop

I have been using my WD external hard drive on my mac at work for the last year or so with no problems. One day I plugged it in and it suddenly did not appear on my desktop. I tried the hard drive on 3 other macs in the building and also 2 PCs and my PC at home. They all access the hard drive just fine. I checked forums for any type of answer and nothing matches my exact problem and none of the suggestions for similar problems have helped. In Disk Utility the drive shows up. The Mount/Unmount button says "Unmount" which I would assume the mac thinks it's mounted. If I click to Unmount and then click Mount it says "The disk could not be mounted. Try running First Aid on the disk and then retry mounting." I then go to First Aid and repair the disk and it tells me that the disk does not need repair. The drive is working fine so I don't want to hear that I need to reformat or something like that. I need to get this working on MY mac ASAP so if some expert has the answer please let me know. Thanks!

The drive is working fine so I don't want to hear that I need to reformat or something like that. I need to get this working on MY mac ASAP so if some expert has the answer please let me know. Thanks!

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You need to calm down a bit if you want help.....

If the drive mounts just about everywhere else but not on your Mac, then we can assume the problem is with your Mac. It sounds like your machine might not be supplying enough power to the drive. Possibly a problem with the USB ports.

So how do I check for a problem with the USB ports and how do I fix it if there is a problem? I unplugged everything but my mouse, keyboard, and hard drive out of the 5 available USB ports on my machine. I tried the hard drive on all the other ports. The mac detects the hard drive in both Disk Utility and System Profiler every time I plug it in. Like I said, it worked before so there must be enough power. Any suggestions?

Do you have any other devices that use USB power (not a printer) like an external optical drive, another hard drive, or even a flash drive to test with?

If you can mount another device and access it from any of your USB ports, then we can assume they're working OK. If at any time your USB ports on the machine were overloaded, the system would shut them down in order to prevent damage. But usually, a reboot after removing the offending device will restore them.

Also, run the Apple Hardware Test. Sometimes that will indicate if there's a problem with the USB or FW ports.

I have used flash drives on these same ports and they work fine.

I have used flash drives on these same ports and they work fine.

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We need to narrow it down between the ports or the drive. And as I stated before, since the drive can be accessed on all those other machines, it makes me wonder if it's something going on with your machine? If not the ports, then what?

I wonder if your drive is suffering from the invisible drive problem? Sounds crazy doesn't it? Take a look at the info from this LINK. Note that although it talks about Tiger OS X, the same has been noted to happen with Leopard and Snow Leopard.

Let me know if that helps.

It's been a while since I've posted. I tried the suggested fix for Invisible Drives and that did not work. After some time I finally purchased a new external hard drive...another WD. Today I plugged it in and I'm getting the same results. Any new suggestions?