To elaborate, my external hard drive suddenly stopped working after working fine for a very long time, I only noticed when I tried to play music from it and it was no longer showing as a drive on my computer.
I checked Device Management from which it had disappeared, and it wasn't showing up in Disk Management either (from Start > My Computer > Manage). SeaTools for Windows didn't show it either.
After a reboot not proving effective, I feared the drive might be broken, and quick Googling suggested I should connect it to a different machine to test that theory. It showed up fine on the different machine, so the next logical step is concluding the USB port itself had suddenly broken down. However, I had already swapped out the external drive with another device on another port, and the other device functioned fine while the external drive still did not.
Finally, I took my keyboard out of a USB 3.0 port and put my external drive in that instead, which surprisingly worked. The keyboard is functioning fine as well, so here I am left without a clue as to how the drive stopped working in the first place. Without this knowledge, I'm not sure how much I should prioritize backing up data form this drive as it would necessitate purchasing another equally-sized drive, which is costly.
The drive itself receives external power from AC, so paired with the knowledge the drive had worked for a year or two already it's unlikely the USB port wasn't providing enough power.
Any help is much appreciated!
Edit: The actual question is if anyone knows what could have happened for my drive to stop showing up, when the USB port and drive both turned out to be fine, taking into account the diagnosis above.