Question : Does the drive still 'start' spinning? .... after connecting the USB lead.

Or do you use an extra power-supply?

Is it possible you touched the on/off switch on the back of the drive? (to OFF)

First thing to do is get them alive again connected to your PC. (Most drives are sold including a 'driver/tools CD)

Check the USB ports on the PC using an USB stick.... if they still work, the port is fine.