Unexpected return from initial read: Volume Corrupt,

In Windows, if you installed a driver to be able to read/write to Linux ext2/3/4 disk partitions, then uninstall it asap, as it corrupts ext2/3/4 partitions.

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Lets quickly check your Ubuntu file system...

• boot to a Ubuntu Live DVD/USB
• open a terminal window
• type sudo fdisk -l
• identify the /dev/XXXX device name for your "Linux Filesystem"
• type sudo fsck -f /dev/XXXX # replacing XXXX with the number you found earlier
• repeat the fsck command if there were errors
• type reboot

Update #1:

• use fdisk to identify the EFI partition. It should be a FAT partition.
• sudo fsck.fat -a /dev/XXXX

Update #2:

Your EFI partition is not fixable by using fsck.fat. It's corrupt.

You can try using Boot Repair, instructions are found here, and it may or may not, be able to fix the problem. You'll need a Ubuntu Live DVD/USB to proceed. Once booted to the Ubuntu Live DVD/USB, you may first wish to manually backup any important Ubuntu or Windows files to an external HDD.

Otherwise you may have a hard disk problem. You can use the Disks application to review the HDD's SMART data, and test the drive, for more info.

If that doesn't work, you'll either have to manually rebuild the EFI partition, or reinstall Ubuntu.

Update #3:

Boot Repair fixed the corrupted EFI partition, and the machine properly boots into Ubuntu again.

I had the same issue with my dual boot of Ubuntu and Windows. In my case, that problem came out after an actualization of Windows that somehow corrupted my boot of Ubuntu. The solution for this headache is quite simple.

Solution:

Note: For this solution USB memory (pendrive) will be necessary. Recommended is an 8GB pendrive that is empty or ready to be formatted.

Steps:

1. It seems to me that in your case the Windows system is the first option to boot automatically if no option was clicked. In my case it was Ubuntu, that was corrupted, and my PC kept switching on and off over and over again. If this issue is happening with any person you can go out of that cycle by holding down F12 or F1, depending on the version of your computer. Then a "Boot Manager" will show up in the screen. Click on option to run Windows boot. If your Windows operating system is working well this step will lead you to Windows and once there you can work on it normally. Put the Pendrive on USB port.
2. Once in Windows, you can download the file at https://github.com/pbatard/rufus/releases/download/v3.11/rufus-3.11.exe. Open it and in the option "SELECT" you will select the .iso you need to download at https://releases.ubuntu.com/20.04.1/ubuntu-20.04.1-desktop-amd64.iso. The last file is big and I recommend download it meanwhile the first one is downloading. For simplicity save both in the same folder.
3. After select the image .iso you downloaded, select the option "GPT" on "Partion Scheme". Click on "Start" and follow the recommended options. This will create a image of Ubuntu in the pendrive.
4. With the pendrive plugged in restart your PC and again hold F12 when iniciate. This time click in the new option that will pop up in "Boot Manager". This is the image of Ubuntu in your pendrive. It will initialize an empty version of Ubuntu and after that select your preferred language and click on "Try Ubuntu". A standard version of Ubuntu in now running from your Pendrive. Connect with wifi to repair the boot of Ubuntu in your PC.
5. Open a new terminal window and paste the command:

sudo add-apt-repository ppa:yannubuntu/boot-repair -y && sudo apt-get update && sudo apt-get install boot-repair -y && sudo boot-repair 

Then follow all the recommended options. Once this is done the boot of Ubuntu in your PC should be ready to work normally again. 6. Restart your computer and select the boot of Ubuntu in your PC. It may take a while but everything should be fine by now :)

Observation: If the pendrive is still plugged in when you restart your PC, a black window may show up asking you to remove your USB memory. Click enter. DONE!