ubuntu-amd-16.04+win8.1 installation

This is my n times to install the Ubuntu os
The main procedure is below:

1. Delete about 500GB sector for Ubuntu os
2. Write the Ubuntu 16.04 os into the U-disk
3. Start from disk (in my computer Thinkstation, press f12) and install the os,
   distribute the following four distribution:
   3.1. /,20480 MB
   3.2. /boot, 128MB
   3.3. swap, 8GB
   3.4. /home, the rest
   4.*important: you should choose the device boot machine to the '/boot' distribution *
   5.reboot the system and then press F12 to choose the ubuntu system boot choice!

And I met some strange problem after installation, however the strange thing.