"initramfs" error on boot ONLY on Dell XPS 13 (boots fine on other computer)

Been struggling with this for a few days now. I am an absolutely green and non-technical Ubuntu user (I like it for it's light-weight/malware-free nature).

I repaired a hinge in the laptop that necessitated disconnecting the laptop from the battery on the mobo. Potentially that changed some of my bios settings?

When I put the drive back into the computer, I began receiving an initramfs error on boot.

If I type "exit", I get: ALERT! UUID=xxxxxxxxxxxxxx does not exist. Dropping to a shell!

I've tried several fixes from around the web to no avail.

Very wierdly, I swapped the HD into another computer (it's an NVMe drive - so a little M.2 drive) and it booted up to my usual Ubuntu desktop/account/etc. without issue. This makes me think there isn't really any issue with my 'fstab' (which I don't actually know how to edit/can't access without swapping the drive into another computer), nor any kind of disk error. I'm willing to try chrisccoulson's solution from this post if any of you think it would help: https://ubuntuforums.org/showthread.php?t=813090

Regardless, I can't boot on the dell. I just get the initramfs/busybox error.

I've tried the following (swapping sda1 for my Linux partition, of course): sudo mount /dev/sda1 /mnt sudo mount --bind /dev /mnt/dev sudo mount --bind /proc /mnt/proc sudo mount --bind /sys /mnt/sys sudo chroot /mnt update-initramfs -u update-grub reboot

No luck.

As additional information (in case it's useful):

• The computer appears to recognize the NVMe hard drive as a bootable device.
• However, the NVMe drive is totally non-visible/not recognized if I boot to a live disk. I cannot edit the drive from this XPS laptop, even from a live USB disk. To edit the disk, I have to move it to another machine and then boot live.
• My thought was to just re-install Ubuntu, but, again, the NVMe drive doesn't show up as an available drive.

When I boot straight from the NVMe on the laptop, I do get the UBUNTU splash screen. So the computer defintely recognizes the NVMe as a bootable drive.

Why wouldn't I be able to see it from a live disk?

This is what makes me think some kind of bios change has occurred that's causing havoc.

I do believe the bios is the most up-to-date version (updated it a few weeks ago). I restored the bios to default settings just in case that might help, but no dice. I checked through the available bios tweaks, but can't see what among them could possibly be causing this.

Something to do with RAM settings? Or maybe I need to reseat the RAM? I don't think so, since I can boot to a live disk. Seems the NVMe drive isn't getting along with Ubuntu.

Another reason I don't think there's actually an fstab issue: I made no change to the data on the drive. I didn't run any updates, nada. I just disassembled some hardware that caused the CMOS to clear/reset. Hence my thinking this has something to do with a bios setting.

I could definitely use some help!

Thanks in advance.

K.O.