Hi drgeoff and DougieLawson
Thank you very much for your help.
> Download Raspbian lite and use Etcher to put it on a card. (No need to unzip the Raspbian as Etcher will handle that.)
I did it today, but nothing changed.
I used Etcher to put the following systems one by one. There was no signal output to display.
> Read the boot problems sticky thread at: viewtopic.php?f=28&t=58151
I've read this article for many times, but I can't find any clue to solve my problem.
(Because I'm new to Raspberry Pi)
Today, I connected the Ethernet, the LED of Ethernet was lighting all the time.
But the ACT LED stopped after flickering about 20 seconds.
By the way, the ACT LED flickers once each time if I press any of the keys(1,2,3,4).
Is there any further information about this problem?