This happened twice so it is reproducible.
I bought a thinkpad A285 (tp) AMD Ryzen on 3/dec/2019. Shrunk windows 10 pro partition and installed 18.04 desktop LTS from USB. So dual boot with windows. Applied all Ubuntu software updates after installation and it was working until 13/Jan/2020.
Then again applied software updates on 13/Jan/2020 and the tp stopped booting with diagnostic sound indicating a failure and with black screen. Lenovo diagnostic app could not identify the code of failure.
Lenovo sent a replacement as regarding it as an hardware issue.
Today 18/Jan I installed 18.04 from USB again same way with windows dual boot. I could login to Ubuntu after installation, then applied all Ubuntu updates as prompted and from software center as well, and the same issue occurred.
Please advise if there were recent updates after 3/Dec/2019 that may break booting or changes thinkpad firmware.
CTL+ALT+F1 shows nothing. Pressing F9 or F12 at power on makes no difference. Connected external monitor with HDMI but nothing showed in the monitor.
Similar to the report at Ubuntu 18.04 bios firmware update for my lenovo thinkpad P50 Crashed