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I had Win8 installed on my computer and needed to install Ubuntu, so I took a distro and created a live usb pen and installed it. Everything went fine, well not at first because my computer comes with secure boot, but in the end it was done 0 errors.

I have grub working now with ubuntu and windows 8 options. I ran boot-repair to fix my problem and it just added another windows 8 option to boot (one on sda3 another on sda4). So the probem is: in either windows 8 grub options, it starts to load normally, then when it should appear the login screen, a blue screen comes up and says a problem occurred and it reboots.

I hope you can help, thank you for your time!

Ps.: I had the exact same problem when I was trying to install Ubuntu and I solved it by deleting the partitions where I was supposed to install Ubuntu. Now I don't want to do it because Ubuntu is now successfully installed in those partitions (ext4 + swap)

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Some secure boot machines cannot seem to boot Windows from grub. A workaround is to provide a different set of EFI files for each type of boot, putting the second set for Ubuntu on a USB stick, and leaving the EFI files on the hard disk for Windows. You have a working Ubuntu set of EFI files already on the hard disk, so take a (small) USB stick (empty, as you will lose all data on it), put a GPT partition table on it, and make a 250M partition for the EFI files. Copy the hard disk's EFI files to the stick. They will appear in the /boot/efi directory, under the directory EFI. Take the EFI directory and all its contents, and put it on the USB partition. I'd suggest editing the stick version of EFI/ubuntu/grub.cfg to change the name of the menu item "Ubuntu" to "Ubuntu on USB" or something to make it obvious which set of files you are booting with. Now try booting from the USB, and see if you get the altered menu item, and that it works. When the USB boot is working, you may simply go to /boot/efi/EFI/Boot, which should be the hard disk's EFI partition, and it should contain copies (possibly with different names) of the Ubuntu versions of the boot files, which should also be in /boot/efi/EFI/ubuntu.
Use md5sum to confirm that you have copies of all files which are in /boot/efi/EFI/Boot, because you are going to delete them! Copy and rename the file /boot/efi/EFI/Microsoft/bootxmgfw.efi to /boot/efi/EFI/Boot/bootx64.efi and you should be able to boot windows from the hard disk again -- remove the stick and try the Windows boot. When you update the kernel, and get a new grub.cfg generated on the hard disk (unused, since the hard disk boots only Windows), you will have to copy it yourself to the USB stick's EFI/ubuntu/grub.cfg.

Hopefully, at some point, the issue of grub not booting Windows on your machine will be fixed, and you can simply replace the hard disk's EFI/Boot file with the ones on the stick's EFI/Boot.

Just make sure you have copies of anything you delete, so you can replace them if necessary. This technique worked for me on a Toshiba.

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