External Hard Drive Invisible?

So I have an external hard drive I use to boot iTunes from since I have enough tv/movies that it was eating up my laptop's memory. Recently my laptop stopped recognizing my external hard drive. It doesn't appear in finder, disk utility, or about my mac. Both my USB ports are functioning and when I plug the drive into a different mac it is happy as a clam and works fine. It also powers on and spins up when plugged into my mac so it's not a power issue. I've done CMD+OPT+P+R and reset the NVRAM nothing has made my mac recognize this drive, what else can I do?

Thanks

update: I have also re-installed the OS and no change

A warm welcome to Mac-Forums, PeridottheClod.

In normal circumstances, I would be tempted to say that your EHD is failing. But then you say that it is all systems go when connected to another Mac.

Before you do anything else, I advise you to Backup (BU) this EHD if it is your only source of all your iTunes & Movies etc. Losing the EHD would be a catastrophe. You can do this using the other Mac. You could just copy the data, one to another EHD; but a better way would be to invest in cloning software like Carbon Copy Cloner (CCC) or SuperDuper! (SD!). Both of these products will create a clone of your EHD onto the new EHD; but have the added advantage of allowing you to clone your Mac's Internal Hard Drive (IHD). This is a great way to BU your Mac and it is bootable.

As regards your main Mac and its inability to recognise the EHD. One thing you could try is: connect the EHD first, then reboot the Mac and see if that works.

Another thing: reset the SMC ( https://support.apple.com/en-gb/HT201295 ). Not sure this will help, but no harm in trying.

But the BU of the EHD is the crucial first step because I do worry about the integrity of that Drive.

Please post back.

Ian

You've been given some excellent advice thus far. At this point I can only add a couple of things:
1. When you make the backup of your external drive play a few files from the backup just to make sure that they have indeed been backed up correctly. No need to load the second files into iTunes just find on of the files, click on it, then tap the spacebar.
2. Try a new USB cable with the Mac and hard drive that are not working together. Perhaps you have tried that already?

Rebooting with the drive plugged in was the very first thing I did when it stopped working, replacing the cable was the second

I reset the SMC and nothing unfortunately.

So now I'm down to cloning EHD, I don't need to clone the internal HDs, both computers already have other EHDs for time machine purposes but the second machine I can't just leave the files on there because they take ups so much space (I have a little over a TB of movies and shows and music, my laptop only has 750gb of storage and the desktop only has 2TB) and the only way I can tell if the iTunes EHD is going bad is to mail it into amazon for warranty purposes. But the drive itself is only about a year and a half old, is drop proof and dust proof and has lived 98% of it's life sitting nicely on my desk.

well it's a problem with my computer. I copied all the files on my EHD to another computer, erased and reformatted the EDH and it's still invisible to my laptop. I've got nothing.