Set /dev/sda2 as boot partition (gparted)

So I screwed up my dual-boot ubuntu and MacOS on my Macbook, when and there are no boot partitions so I’m currently trying Ubuntu from a USB

I can see the original MacOS partition in GParted, it’s in my /dev/sda disk but it’s inbetween two unallocated partitions; Unallocated (200MB) – /dev/sda2 (83GB) – Unallocated (29.7 GB)

I right clicked my MacOS and selected the boot flag, but it won’t recognise it on boot.

How do I tell it to use the /dev/sda2 partition as the boot partition? :S

Error mounting /dev/sda2

I have a problem with a hard disk. This used to be in my Lacie Network Space 2, but it crashed.

Under windows I don’t get to see anything, of course, so I ordered a USB – SATA cable, and a live boot usb from Ubuntu.

So far what I have done. Because otherwise I am a layman and I try everything to get my photos / videos back ..

To be precise, when I start Ubuntu, I get the following message when I click on the disk.

Error mounting / dev / sda2 at / media / ubuntu / cea89a46-6cf3-492e-80f3-d270280237ac: can’t read superblock on / dev / sda2

Who can help me,

install checking /dev/sdb and my OS is on /dev/sda2

Ok so in the installer I have no option to install ubuntu alongside windows (I have windows 7) after clicking on “Something else” I can see that my windows is installed on /dev/sda2 and the installer didn’t notice it or something I think it checked /dev/sdb for my OS but it didn’t find it so how can I change it to notice my OS?

My installer doesn’t even detect the OS and I see every other option it says that it didn’t detect ant operating systems I already have “taken” some memory and have Free space (100GB)