Thanks for @harrymc's hints. It seems the issue is caused by the connection sharing between my real ethernet adapter and VirtualBox's "host-only" ethernet adapter, which is once setup before. Here is my solution.
I opened the device manager with "Show hidden devices" checked. Surprisingly, I found "VirtualBox Bridged Networking Driver" still existed even if I had no VirtualBox on my machine. I disabled all of them, then my connection lost immediately. Then I installed VirtualBox again and this time I met no obstacles. But I soon found that the internet connection was still blocked. I checked Network Center, only to see VirtualBox's card was working. So I uninstalled VirtualBox and had it installed for the third time, after which all runs perfectly.