Usually if you get the grub boot loader and it doesn't show any boot options, it's because grub was not installed correctly and/or the partition that it is supposed to be on has changed or does not exist. It can also happen if you install Linux to one drive, but the boot loader to another by accident, whether EFI or MBR/Legacy mode.
You can normally fix it by chrooting into your root partition:
#become root
sudo su
#make a directory called target where we will mount your root partition
mkdir /target
#mount /dev/sda3 to target (change to match your root partition)
mount /dev/sda3 /target
#if you are using EFI mount your EFI partition to /target/boot/efi (assume here it is /dev/sda1)
mount /dev/sda1 /target/boot/efi
#we need to mount dev proc and sys for the chroot to work like it was booted normally so we can fix it
for mount in dev proc sys; do
mount -o bind /$mount /target/$mount
done
#now chroot
chroot /target
#run grub install on the drive that you installed Linux to
grub-install /dev/sda
linux, grub, loader, solutionusually, doesn, installed, correctly, partition, install, efi, mbr, legacy, mode, chrooting, sudo, su, directory, mount, mkdir, dev, sda, proc, sys, chroot, booted, bind,