My External hard drive fell and not showing up on Mac 1 week back my 1TB Seagate Expansion external hard drive which I used for Time Machine backup fell on ground. I freaked out and immediately connected it back to Mac. and to my horror the drive didn’t showed up neither desktop nor on Disk utility. I checked it again and found that the light was still on. There were no sounds which indicate physical damage I mean clicking, buzzing, tickling or damaged component sound. I looked on the web to scan this hard drive with some software and found this link http://www.stellarinfo.com/support/kb/index.php/article/recover-mac-time-machine-drive but again the drive isn’t getting recognized by the software. Thisa drive is no longer in warranty. Could someone let me know how should I open the hard drive safely? What tools I might require? Will changing the enclosure bring back this drive? I still believe the hard drive might be OK since there is no signs of physical damaged and its light is still on. Please help ….
The drive enclosure may be broken, but it could also be the drive itself, being the logic board or head. It's more likely the drive is broken if it was powered on when it fell. Since it's your backup drive, you hopefully haven't lost anything critical. I'd start thinking about getting a second backup drive to reduce your exposure to loss.

Most USB externals are fairly easy to take apart with a screwdriver, and just have a standard SATA drive inside of them. If you have a SATA to USB adapter you can test it, or even better is to connect to an internal SATA to verify S.M.A.R.T. etc. However a 1TB drive is pretty cheap now, so you might just replace instead of trying to repair.