Context: I have always had trouble installing Linux in my ACER SPIN5 SP513 Series. For installation I have to "Select an UEFI as trusted for executing", then EFI, then BOOT and then 'shimx64.efi' and place it a the top in the the Bios and in that way I installed some distros, ultimately Ubuntu because I have noticed that my pc was turning slower. In the image, "Linux" (not the best name) was the select UEFI that I had before, it was Ubuntu and I don't why it is there, I have reset the settings a couple of times. 

[![usual order for booting and it worked pretty well](https://i.stack.imgur.com/ZGBvw.jpg)](https://i.stack.imgur.com/ZGBvw.jpg)

I wanted to install a lighter distro but when I tried with Lubuntu and Lite, I couldn't even enter to the installer, because after doing the process I mentioned, I couldn't see them via F12. After a couple of times, I decided to try Fedora but this time with Anaconda Installer, I couldn't see my SSD, just the bootable device (the USB).I tried with Ubuntu20 and displaying that I only had 4 Gb of space (the USB). 

I have seen a couple of similar posts but I don't actually know what to do. [This](https://unix.stackexchange.com/questions/414889/fedora-not-detecting-my-hard-drive-when-installing-fedora-27) was possibly the most concise solution but I don't know how to change my SATA OPERATION, also, in the BIOS 'Information' appears:

```
HDD Model Name:         None
HDD Serial Number:      None
SATA Mode:              AHCI

```

So... that solution might not work. Also I tried:

```
sudo dmraid -r -E /dev/sda
no block devices found

```

This is the actual state of my disk: 

```
sudo fdisk -lu /dev/sda 

```

[![Can't see my SSD! ](https://i.stack.imgur.com/1ThQu.png)](https://i.stack.imgur.com/1ThQu.png)

In conclusion, I'm quite lost and my questions are: 

1. What could be a cause of the "disappearance" of my SSD?
2. Why can't I see it?
3. What is dmraid and what can i do with it?
4. What is AHCI and RAID? and what are the differences among them?
5. Most important, how can I fix this, installing a distro and leaving my pc as it was before with Ubuntu 19.10 or any other distro?
Extra:
6. Do you have any idea if there is anyway of updating my BIOS in order to make more efficient the installation process of GNU/Linux distros?

Sorry for the long post and lots of question but there are many concepts that can be explained, that beginners as me might not understand. I hope you can help me and thanks in advance!

[Plz, if I need to edit something in my post, I would gladly do it! Just starting in this community and feedback is relevant to me]