I've got an Leonardo board, it seems to be official, in that it has the Arduino branding and Made In Italy on the bottom.
However I cannot get anything to run with external power supply. Everything when powered via the USB from the computer runs fine. As soon as I use any sort of external power, and I've tried both the barrel jack with 4x AA batteries, 6x AA batteries, 9v square battery and a Shield with 2x 3.7v lithium batteries - it turns on but doesn't do anything - the USB device doesn't even appear to the computer at all unless I pull the external power out again.
Is this a faulty board? Do I need to change the jumper arrangement on the board so it'll run with external power?