Lenovo W541 black screen after installing more RAM

I installed more RAM (16 GB → 24 GB) by adding leftover two known-good 4 GB sticks to the factory installed two 8 GB sticks. I was mildly worried that the Lenovo W541 turned on to a black screen, no response to Fn keys, no Fn Lock LED, no mute LED, couldn’t get the keyboard to light up beyond the initial flareup/flaredown.

I had to wait 45 seconds and the system restarted normally. It seems there’s some kind of self-check the laptop runs once upon RAM size change. Too bad they don’t put a “RAM testing” notice on the screen to avoid panic of the user!