By default, Jetson Nano power up using the Micro USB.
To power up using 5V DC Barrel Jack, you need to set the jumper on J48: Power Selection (next to J25: Power Jack). There is only 2 pin, so just put the jumper on both the pin.
The board design is slightly different for rev A02 and rev B01. Refer to Jetson Nano Developer Kit User Guide 1.3 2020/01/15.
If power up is successful, there is a green LED light besides the Micro USB.