I've got an SSD (c),an internal HDD (d), an external HDD (e) and a USB flash drive (f).
How this all went down:
I downloaded Ubuntu and used a program to install it on my (F) drive.
I reset my computer, ran the (F) drive for boot, and installed Ubuntu.
I reset my computer, and it forcibly automatically booted into Windows 10 instead of Ubuntu.
I went into Windows 10, and used a program called Easy BCD, by NeoSmart. I followed their guide, but after step 6, it wasn't the same for me.
Their guide said that upon rebooting, I should see a grub screen that lets me choose between Windows/Linux and a few other options, however my computer would only boot into Windows 10.
I decided to follow the rest of the guide regardless, however by the end it would let me boot 'windows' or 'linux', but the linux option would always break. It went to a screen with lots of commands, that I thought -may- be a barebones Linux or something, but it definitely wasn't Ubuntu.
I decided to reinstall Ubuntu using the USB flash drive.
Upon resetting, no matter what hard drive or format I select for booting (besides the F drive), it says
An operating system wasn't found. Try disconnecting any drives that don't contain an operating system.
I can boot the F drive and run Ubuntu, but it's a one time version that doesn't save any of my data. When I went into the installation, it still says that I already have Ubuntu installed on the 4TB HDD and that I have Windows 10 installed on the SSD, however I cannot seem to boot into either of them.
TLDR: Windows 10/Ubuntu are both installed, Windows on the internal SSD and Ubuntu on the external HDD. Ubuntu's installation program on the (F) drive recognizes them, however, when I try to boot anything it says
An operating system wasn't found.
When I press F11 and force it to boot from the SSD it says:
error: no such device: 83b6c64d-9a2c0467b-a02c-6374ee6ac3dc. error: unknown filesystem. Entering rescue mode. . . grub rescue> _
and it will allow me to type some commands.