The Ubuntu16.04 used has been stuck in the "Loading initial ramdisk", only the recovery mode can be entered. Upgrade to 18.04 and change the kernel will not solve the problem.
After entering the system through recovery, execute "sudo apt install intel-microcode=3.20180312.0~ubuntu18.04.1" and the system starts normally. Refer to: https://askubuntu.com/questions/1145856/ubuntu-18-04-fails-to -boot-even-in-recovery-mode-stuck-on-loading-initial-ram-d
However, there is no GRUB menu, so the GRUB menu can be displayed again by modifying /etc/default/grub.
