I tried a new cable for my external hard drive, and now it won't mount anymore with the old cable.

"I tried a new cable for my external hard drive, and now it won't mount anymore with the old cable.: [...]It shows as a top-level device in Disk Utility, so I can't mount it. It also shows in system information.[...]"

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Mounting this Drive:

It is seen, but your are unable to mount it? It would try booting into Revery Mode, and then viewing Disk Utility there, seeing if your can moon it.

Download a copy of the diagnostic app DriveDX from Binary Fruit and see what it has to say about your external drive. They don't last forever. Ten years is a good run for a hard disk drive.

Get yourself a new drive so that you have something to copy your files to if you finally are able to mount the old drive again. There's no telling how long the old drive will remain accessible.

"I tried a new cable for my external hard drive, and now it won't mount anymore with the old cable.: [...]It shows as a top-level device in Disk Utility, so I can't mount it. It also shows in system information.[...]"

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Run First Aid:

While in Disk Utility, select the drive, and then use the First Aid button

Did you purchase the cable online? If so, can you provide a link?

When trying @D.I. Johnson's suggestion of DriveDx, make sure to use the original older cable that had been working. You will need to install a special USB driver in order to allow the necessary communication with the external drive to access the drive's health information.

Have you tried rebooting the computer? Sometimes a simple reboot will fix odd behaviors.

And disconnect all other external devices. If you have a USB3 hub, then try connecting the drive to that since I've seen some reports on this forum where some M-series Macs seem to work better in that configuration with some drives.