Recently, I installed PrimeOS (Standard version) onto my computer in its own ext4 partition. During the installation it asked if I would like to install GRUB2, obviously unaware that my computer already had it. This attempt to install Prime is only just after a nasty encounter with Android-x86, where a new GRUB was installed without the option to boot my preexisting operating systems (an affair that ended with my completely wiping everything and starting afresh, since even BootRepair didn't fix it).
Because of this I chose to skip that step, and of course, this means that I cannot boot Prime as it doesn't show up in my GRUB menu (or the BIOS boot menu, for that matter).
I've tried using BootRepair, but on looking at the advanced setting it appears that it doesn't recognize it as an OS to be booted at all. I read this article, which helped me to get at least a basic understanding of GRUB. I began following this guide, which seemed promising, but the steps seemed strange to me, since he was using the ISO for the live USB installer, and one comment says that it doesn't save any data, just like a live USB would.
It did help me find out about GRUB Customizer, though, and this is what I've been looking at. In-so-far I've just used the default boot sequence:
Which gives an error, unsurprisingly. Anyway, any guidance on this is appreciated. The computer in question is a 5-year-old HP Pavilion Notebook, with Linux Mint Debian Edition 4 installed already, and working fine. Cheers!