Hello world!

I have a laptop Toshiba L50-B-1FH. It come with pre-installed Windows 8.1

Three years ago I installed Ubuntu 16 LTS without any problem, with dual boot. One month ago I tried to start Windows again to use a special application only compatible with Windows and Windows SO didn't start-boot, just black screen.

Here my grub and fstab setup https://paste.ubuntu.com/p/TjnTJksdFx/

Then I used boot-repair application to try to fix it. Here current grub and fstab setup https://paste.ubuntu.com/p/DsZvtWPGMd/

Boot repair application tell me to go in BIOS and select sda2/EFI/ubuntu/shimx64.efi

When I restarted computer more entry are available now "Windows Boot Manager" "Windows recover", mmx64.efi appear and Ubuntu as always but except Ubuntu that start linux normally I get black screen in all other entry.

I tried to enter in BIOS but almost all entry are greyed, not selectable. No option of supervisor password. More Toshiba users have experienced similar problems with no very good result.

What can I do to recover dual boot? Is it GRUB problem? Is it Windows problem? Is it BIOS problem?

My opinion is that maybe some Windows 8.1 update blocked the BIOS with some secure UEFI topics damaging boot. Is it possible?

Using linux/windows for more than 10 years and first time I am not available to fix problem by myself.

All suggestions and help is welcome. Thanks

What does sudo efibootmgr show?

What is this boot repair deal you are talking about?

Also you could get a Windows 8 or 10 dvd and boot to repair it or view issues.

The free update to windows 10 may have been useful.

You have both windows 8 and Ubuntu installed UEFI and your EFI partition shows the correct files for each. You have also installed Grub code to the MBR which is not used or necessary. Are you certain you have the BIOS set to boot UEFI as it needs to be. I'm not familiar with the Toshiba BIOS, do you have a Boot Option to boot from EFI file? If so, look for the /EFI/ubuntu/shimx64.efi

Your grub.cfg is correct and it also has an entry for windows which is correct.
Do you have Secure Boot on?

boot-repair tool is SW developed for Linux that solve most of boot problems automatically https://sourceforge.net/projects/boot-repair/

I confirm BIOS was setup in UEFI mode and with secure boot, but options were greyed not selectable. I realized that /EFI/ubuntu/shimx64.efi was loaded by BIOS correctly.

So after yancek's confirmation that grub was OK, I follow jefro's suggestion and I used recovery DVDs created the first day I bought the computer (thank god I'm a back up maniac). This DVD is basically Windows 8.1 for Thoshiba, I selected the option only restaure SO keeping file users.

Then BIOS was accessible again and Windows 8.1 started normally but without applications I installed. Next step was to create and booteable CD with supergrubdisk from https://www.supergrubdisk.org/, I started my normal Linux SO and I run boot-repair. Now Windows and Linux are accesible again.

Summary,Windows 8.1 was broken maybe because some update or incorrect power shutdown, I restaured Windows and install grub again. Thanks for the help. [solved]