My old laptop broke, so I took the HDD and bought an external HDD case to recover my files. At first it worked greatly, but recently when I plug it into my laptop the hard disk is not detected. The hard disk is spinning but the light doesn't blink or even glow at all.
If it were mine, I would try to connect it directly to a motherboard and see if it is detected in the BIOS - it's possible the controller has gone bad and is no longer working to the point of being detected - this would rule out any problems with the external hdd case.
Another way to test, if you have another working laptop drive you can connect to the adapter, if that is working but not your original drive that can also be another indicator that the drive is truly dead.