The computer has enough horsepower and RAM.
- What about Windows and BIOS or UEFI? If UEFI, things are more complicated than with old style BIOS.
- Optimus is also making things more difficult. There is Bumblebee ... search the internet for linux bumblebee and find information about it.
Maybe you installed grub into the wrong place, either to the wrong drive or to a partition instead of the head of the drive.
You have three options:
1. Reinstall and use 'Something else' at the partitioning page. It gives you better control of what is happening.
2. Repair grub according to this link
3. Run Boot-Repair and let it do it's job. In this case I suggest that you disconnect any drives (even internal drives) that you do not want to involve in the repair job.
sudo mount /dev/sdXY /mnt # Example: sudo mount /dev/sda5 /mnt
sudo grub-install --boot-directory=/mnt/boot /dev/sdX # Example: sudo grub-install --boot-directory=/mnt/boot /dev/sda