I found a strange thing when given a less than a year's raspberry pie 3B + reinstall the official system, raspberry pie cable network will be automatically stopped after the restart, the wireless module only normal. That network icon in the upper right corner displays a red cross.
After many unsuccessful reloading and found a command that allows a wired network card recovery
sudo ifconfig eth0 down sudo ifconfig eth0 up
In fact, it is to reboot the network card eth0
Later, the Raspberry Pi unplug HDMI output line, after connected to ssh access, then restart it dropped the card has not had any problems, so the suspect is connected to the HDMI monitor output signal to start the wired network card caused a disturbance.