I have recently received a parcel containing a Spresense kit (main board, extension board and camera module) but unfortunately have been unsuccessful in getting it up and running. I was following the tutorials on your website to connect it with my setup (Ubuntu 18.04 64-bit + Arduino IDE 1.8.16).
If I plug a USB cable to the main board's micro-USB connector, the power LED does not light up although the serial interface ttyUSB0 appears (dmesg | grep "cp21.*attached" even returns usb 1-1: cp210x converter now attached to ttyUSB0). Alternatively, connecting to the expansion board's micro-USB connector lights up the main board's power LED, but the serial interface does not show up.
I've tried nonetheless to burn the bootloader via the Arduino IDE or returning to factory default settings via your recovery tool but neither have solved the issue.
Do you have any insights with regards to this? BTW I tried with different USB ports / USB cables / computers.
Thanks for your help!