My external hard drive suddenly stopped showing up on my Mac, even though it appears to power on when connected. It contains important files I need to recover. What can I do to safely access the drive without losing any data?
If the drive is clicking, beeping, repeatedly spinning up and down, or disconnecting every few seconds, stop powering it on. Software recovery can make a physically failing drive worse, and important files may justify sending it to a recovery lab.
If it sounds normal, start with checks that do not write anything to the disk. Try a different cable, port, and powered adapter if the drive uses one. Avoid an unpowered USB hub. In Finder, check Settings > General and Sidebar to make sure external disks are enabled. Then open Disk Utility and choose View > Show All Devices. Check System Information under USB or Thunderbolt too. That tells you whether the Mac sees the hardware even if Finder cannot mount the volume.
If Disk Utility sees the physical drive but the volume is grayed out, try selecting the volume and clicking Mount. Do not click Erase or accept a prompt to initialize the disk. I would avoid running First Aid as the first recovery step when the files are irreplaceable because filesystem repair changes disk structures. Ideally, create a byte-for-byte image or clone first, then work from that copy.
When the device appears in Disk Utility but will not mount, recovery software such as Disk Drill for Mac may be able to scan it for files. Save recovered files to a completely different drive, never back onto the problem disk. If the drive is unstable, imaging it first is safer than repeatedly running full scans against the original.
If it does not appear in Disk Utility or System Information after testing another cable and another Mac, the problem may be the enclosure, USB bridge board, power supply, or the drive itself. A replaceable enclosure can sometimes be the cheap fix, but be careful with models that use hardware encryption through their original USB board. In that case, moving the bare disk to a generic enclosure can make the data unreadable even when the disk is healthy. For genuinely important files, that is the point where experimentation becomes riskier than professional recovery.