Ubuntu – System can not reboot after completing installation

First, look for an updated firmware from your manufacturer. (It will probably be listed as a "BIOS update," although it's not really a BIOS.) After updating, you'll have to re-register GRUB with efibootmgr. With any luck it will start working; however, don't get your hopes up, since these updates seldom do any good.

Another option that sometimes works is to set the default boot option via Windows. You can do this by opening an Administrator's Command Prompt window and typing:

bcdedit /set {bootmgr} path \EFI\ubuntu\shimx64.efi

If neither a firmware update nor setting the Ubuntu boot loader as the default using Windows helps and the computer is new, I strongly suggest you return it to the store for a refund, on the grounds that the behavior you're seeing is a design defect. Manufacturers will continue delivering machines with that sort of defect if they don't feel the pain of doing so, and the only way they'll feel any sort of pain is if machines are returned and they know why.

If the machine is too old to be returned for a refund, your only choice is an ugly shell game with boot loader filenames, as I describe on this page of mine. This is most easily done via Boot Repair, which provides an option to do such renaming and reconfigure GRUB appropriately on its Advanced menu. The option is called something like "back up and rename EFI boot files" (but that's from memory; the exact wording is almost certainly something slightly different).

The installation is asking you to remove whatever media (e.g. USB drive, CD, DVD, etc) that you used to boot the installer and then press the Enter key to reboot the machine.

This way it won't boot into the installer again.