Computer Won't Boot from Proper Drive

[ChapyYxx]

For over a year now I've been booting from my SSD, without issues. However, I left my computer on today when I went out. When I came back, I saw I was on the Windows login screen. I put in my password and realized that it booted from the wrong drive - my hard drive I used previously. The SSD still shows up in the My PC tab, and it also shows up in the BIOS. That's what I find strange. The drive is there and the computer knows it, however when I look at the boot order it's all normal. The SSD is first, then the hard drive. I tried disabling the hard drive in the boot order, but then it boots and says "Reboot and select proper boot device" (Or something along those lines). All the files on the SSD are still there and I can access them when I boot from the hard drive.

The board I'm using is an MSI G series board, if you're wondering about the BIOS.

Thanks.

 

[SkyNetRising]

Can you post screenshot from Disk Management?

 

[ChapyYxx]

Can you post screenshot from Disk Management?

https://drive.google.com/open?id=1C5aopr1Up5Psa2z0rXT00iFpcwIQ0k1x

 

[SkyNetRising]

Windows on Disk 0 is installed in legacy/csm mode.
Windows on Disk 1 is installed in UEFI mode.

If you have disabled UEFI boot in BIOS, then you'll not be able to boot from Drive 1.

Are windows on both drives the same version?
You could add bootloader entry for windows from Drive 1 to bootloader on Drive 0 with bcdboot command. That way - with single bootloader you could boot both OSes.

 

[ChapyYxx]

I haven't disabled UEFI, the boot mode is "UEFI + Legacy," which is what has worked in the past. I'm confused as to why this problem popped up so suddenly.