This is a longshot but maybe someone would be able to help me with this. I have a laptop that only has a single NVMe drive. I booted it up today to find "Checking media presence......." after the splash screen and then it booted into BIOS. The BIOS doesn't see the NVMe device. I don't understand how this could've happened because I didn't update anything or change any setting or physically damage or jostle the laptop between the last successful boot and clean shutdown and now. When I boot into an EndevourOS liveusb, the installer can see my entire drive and its associated partitions. I can't access them though, I think because they're encrypted, but even so I feel like I should be able to see them in the filesystem, as I've rescued files like that before (from non-encypted drives). So I can't really make heads or tails of this. If the liveusb is seeing the drive and the correct partitions, it can't possibly be physical damage to the drive itself, right? Or any of the connections? Yet BIOS can't see it for some reason and won't boot into it. If it's worth anything, the OS on it is Arch with grub as the bootloader. Obviously I've tried to reseat the drive, move it to the other available slot, I've toggled on and off all sorts of settings in the bios, and nothing makes any progress. If anyone has any ideas, I'd be grateful. Thanks!
Editting to add: I'm not entirely sure the BIOS doesn't see the device. The menu is fairly unclear. There's a series of lines starting with "NVMe Device", which the corresponding entry is just blank. Then there's two lines of "NVMe Controller", one of which has an entry that I can't select or see more of that says "SAMSUNG (5...", which makes me wonder because my NVMe drive is 512gb, and I wonder if it's listed there? But I can't see anything beyond the elipses so I can't tell. Then the other controller line just says "Empty". Not sure what to make of that.
Second edit: There's a section in BIOS for RAID disks, and in it there's a listing for "Non-RAID Physical Disks" in which my NVMe drive is listed correctly. So maybe it's a bootloader thing? I'm so confused.
Final edit: Thank you so much for the help everyone, even though I'm sure my post was a confused mess. I luckily managed to back up all my files, so it's just a matter of fixing grub or reinstalling at this point. I hate computer :)
The UEFI firmware stores a list of boot loaders in NVRAM (a dedicated chip on your motherboard) in what are called EFI Variables. Sometimes this gets fucked up if the drive numbering changes, like when a drive is added or removed (physically, or "effectively" due to power failure or some other freak incident), or if it is snowing outside, or if the machine is booted on Friday the 13th in an even numbered year. It sounds like rather than GRUB just disappearing, the EFI variable pointing to it has. You might just need to re-create this EFI variable. The tool for this is efibootmgr. Though it can be helpful, you don't actually need to do this from a chroot environment. You could do it from any rescue CD (if you need to re-install GRUB, then you should do it from a chroot though).
The UEFI firmware usually will make no attempt at auto-detecting bootloaders (with the possible exception of
BOOT\BOOTX64.EFI). The OS installer creates an EFI variable at install-time, and if it becomes invalid for whatever reason it gets yeeted.