16.04 LTS does not boot, graphic resolution on screen low
Grub 2 (GNU GRand Unified Bootloader 2. Generation) is the tool that rules the Boot order in the Linux Machines
We try to give here some tips on the different problems you may have with it. You can find an overview under https://help.ubuntu.com/community/Grub2 and its configuration possibilities under https://help.ubuntu.com/community/Grub2/Setup#Configuring_GRUB_2