After two years of using 14.04 LTS I went to install it on my desktop, but wanted a newer ISO and was surprised to see the new 16.04 LTS sitting front and center a few days ago. So I said what the heck, may as well enjoy the new stable release. What was I thinking in putting stable and long-term in the same category for a release this new?
Anyways, after having to reinstall due to an infinite login loop after updating my Nvidia proprietary drivers, I finally got my system back up and running, then I decided to fall back to 14.04 LTS and wait on the upcoming 16.04.1 (if not much farther out) update(s). Problem is, my Grub2 boot loader is gone. I can't boot into Ubuntu at all.
I tried the boot-repair and even deleting grub2 with Windows repair disk, but I am still getting a broken grub2. I want to get this resolved before installing 14.04 LTS.
Boot-repair gave me this link.
I am running a Core i7 4771 CPU, 2GB GTX770 GPU and 16GB DDR3 Gaming RAM with two 1TB 7200RPM HDDs for storage. My Windows 10 (less than 200GB total) and Ubuntu are both running on the first 1TB and Ubuntu has a 16.3GB swap set up just for giggles. I am running 14.04 LTS on my Dell Inspiron M531R-5535 with zero issues and have even repaired the grub once, but I can't remember what broke it. I am not sure what is the problem.
Best Answer
If Windows is UEFI, you need to install Ubuntu in UEFI mode. How you boot install media from UEFI/BIOS is then how it installs.
But if you have installed in BIOS boot mode, you can convert from BIOS to UEFI without reinstalling by uninstalling grub-pc(BIOS) and installing grub-efi-amd64(UEFI) and some settings changes. Boot-Repair in its advanced mode makes this relatively easy with the full uninstall/reinstall of grub. Be sure to boot Ubuntu installer in UEFI mode, and add Boot-Repair.
https://help.ubuntu.com/community/Boot-Repair
Details on screens in Boot-Repair:
https://sourceforge.net/p/boot-repair/home/Home/
How you boot install media from UEFI may not match default boot settings in UEFI for the actual install. Make sure you always boot in UEFI boot mode and have settings for UEFI.