Nano works fine powered via microUSB but shuts down after a few seconds on barrel connector. Specifically, it displays the NVIDIA logo and then it shuts down, power LED goes off. Tried 4 different power adapters including 9A one. No peripherals attached. Didn’t forget the jumper. Fails the same way if I bring power directly to the GPIO pins. Fails the same way whether monitor is or isn’t attached.
Do you have a 5v 4a power adapter that’s known to work here on the forum? The nano is sensitive with ac adapters. FWIW this is the one that works for me. If you google, there are more threads on this forum with people reporting what works and what doesn’t. If you do have one that works on the forum, have jumped j48, and it still doesn’t work, I would RMA the device.