BootDevice Not Found - acer aspire s7

[Şerban S.]

Hello!

[...] I have 3 partitions (4 with the usb key)
dev/md126 : unallocated and unrecognized partition table
dev/sda (usb key)
dev/sdb : none partition table
dev/sdc : none partition table

It looks like the storage dev/md126 is the problem.
As it appears, you have 4 different storage media (dev/md126, dev/sda, dev/sdb dev/sdc).
I only encountered this once long time ago, when SSHD was somehow common on the market.
The listing is abnormal, since the internal storage is unrecognizable, coupling that with the previous messages, my conclusion is that you have a soldered (onboard) SSHD and the buffer partition (the SSD, dev/md126) is gone. That means the internal drive is gone. If there is another way to check this, please, do so.
In another environnement if the internal drive was functional, it would be listed as dev/sda/, but you said the dev/sda/ is an USB drive (stick).
This only happens if the main drive is damaged.
Assuming I am wrong, then it is possible that the unallocated space is usable, but without knowing the available space on each partition, it's impossible to make any educated guess.
I need to see the whole GPartEd screen to understand what is happening there.
Take a picture of the entire GPartEd screen and post it here.
You can also try to create a new partition on /dev/sdb/.
Bunt since I have no clue on the size of the media it's impossible for me to figure out what to do with so less information.


Sample screens:

1. The GPartEd main screen, showing main drive's partitions:

As you can see, the partitions, are listed like /dev/sda1, /dev/sda2, etc. and with the respective sizes.

2. The GPartEd main screen, showing the list of drives:

3. The GPartEd main screen, showing the drive's /dev/sdb partition:

I hope now you understand what I need to figure out what is happening out there.

Meanwhile, search on YouTube any video regarding "Using GPartEd beginner tutorial" and study the partitioning process.
Take a look at this one:

https://www.youtube.com/watch?v=O5kh_-6e4kk

In your message you mixed all the information you remembered, regardless the meaning.
So, I can only guess that the main drive is /dev/md126
Post the screen images and we'll se what can be done.

Best regards, Șerban