Seems that this isn't as straight forward as the internet makes it.
First things first, some key things about the laptop:
2 physical hard disks, one is a 250GB SSD and the other is a 300GB HDD,
Windows 10 was installed first on the SSD and the HDD was used as a storage drive for Windows,
Secure boot was enabled, but read the post below for an explanation.
I grabbed a copy of elementaryOS from their website and used Universal USB Installer to make the flash drive. That went smoothly, so I booted into the pendrive straight away without changing anything in the BIOS.
Installation goes as expected, but then I hit one of the first "bumps" of the install:
When it lets you choose the partitions and drives to install to, it only let me choose the 300GB HDD storage drive. Didn't think much, allocated it some space and continued.
When the installer asks for permission to install some drivers and these so called proprietary drivers. I checked that, but then it asked me to create a Secure Boot password. Didn't think much, made that.
Everything after that went swimmingly! The OS was installed and it asked for a reboot. The system rebooted and I removed the pendrive from my laptop. The computer booted straight to elementaryOS and asked me to log in. When I tried to log in, it would just give me a black screen and straight back to the login screen. I couldn't even CTRL+ALT+F3 or whatever the command is, to get to the command line and edit the Xauthority file. No way to reboot the computer either, so I do a hard reboot via the power button. Upon doing that, I got something like this on my screen (see the pic below).
Not knowing what to do or how to get out of it, since it did that at every restart, I hard restarted it again and mashed ESC to get to the boot sequence selector and selected Windows Boot Manager. It booted Windows just fine and whenever I start or restart my computer after Windows is loaded, the GRUB menu shows up as intended, and let's me choose elementary again, but the result is the same. Keep in mind, that secure boot is still enabled.
Any ideas on what could be the fix? How would I go about uninstalling Linux and GRUB and just going back to Windows and trying again? What things do I change, to make it work?
Sorry for the long wall of text, running out of ideas here. :(