This night I completely unplugged my Linux SSD and reinstalled Windows on another hard drive.
I plugged in the Linux-SSD again after the installation, but when I tried to boot it my computer wanted to boot to Windows. I went to the BIOS and changed the boot order back to how it was before (my machine always booted to Linux on default). Normally I'd be shown GRUB 2.0 for some seconds, but then my Windows wanted to repair the Linux drive (!), on which screen I immediately pressed the reboot-button. My Windows shouldn't even touch my Linux-SSD, that's why they are on separate disks ...
I went to the BIOS again and set the Boot Mode to
UEFI only (I actually believe it was on
UEFI and Legacy before on the working machine).
After this, my computer prompts
"Reboot and Select Proper Boot device or Insert Boot Media in selected Boot device and press a key"
Before the windows-reinstallation I had to manually chose to boot from the Windows-SDD, as Windows didn't even had an entry in the GRUB (for maxmimum separation within one case).
Can someone explain me what happened to my Linux drive or the bootloader of which I thought it was located on the Linux partition, and how I can fix this to boot to Linux again?
Might it be that Windows made some changes to the BIOS so the BIOS doesn't find the Linux bootloader?
Additional info/status quo:
efivar-tester in arch-chroot:
About to test empty [runs through] About to test one skips at: testing efi_get_variable() FAIL: "one"(line 212) (-1) get size test failed: wrong size: 1 should be 2 (append may be at fault)
I am inexperienced with EFI.
modprobe efivars on Live system:
modprobe: FATAL: Module efivars not found in directory /lib/modules/4.16.3-301.fc28.x86_64