Hi FLOOD, richbuff,
Suddenly, both of my PC can login Gmail now.
I have reinstalled the 2nd and installed Avast so as to continue use Gmail. Because of GIS report I reinstalled KIS. I expected GMail will fail again but it works normally.
I then checked the 1st PC, it works normally too. I really didn't reinstall KIS or anything on the 1st PC.
Although don't know the reason, my problem gone anyway.
Thank you for your effort these days.