Why isn't my old hard drive connecting to my new computer?
Solution 1:
The standard 3.5" HDD needs a 12V supply to spin the motors.
If you only have USB connection, there is no 12V supply provided to the HDD, so it does not work.
2.5" HDDs work with single 5V supply.
Typically adapters intended for use with 3.5" HDD drives come with an external 12V power supply.