Obviously you need to repair your EFI booting.
It can be happens if:
1. Was reinstalled system.
2. Your UEFI partition was broken, formatted, or erratic cleaned.
Exist nice solution for this:
terminal and type:
sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update
Press Enter key, and wait for completion. Then type:
sudo apt-get install -y boot-repair && boot-repair
Again press Enter key, wait for install completion and program running.
For next steps refer to this links:
Ubuntu Documentation - Boot-Repair