First, try disabling Secure Boot. Although Ubuntu theoretically supports Secure Boot, there are still a lot of problem reports concerning Secure Boot, particularly in dual-boot configurations. I think it's unlikely that disabling Secure Boot will immediately solve your problems, but it will make it more likely that any given thing you try to fix your problem will succeed.

Second, there are a number of things you can try to fix your boot problem, including:

• Install my rEFInd boot manager. Note that there are USB flash drive and CD-R images you can try before trying the whole thing; however, they won't boot your Linux kernels directly unless you hit F2 or Insert twice and add ro root=/dev/sda9. If you install the Debian package, you should no longer need to do this. The USB/CD-R images should also boot both Windows and Linux via GRUB successfully.


• Run the Boot Repair tool. This program can fix a lot of boot problems, although it does sometimes fail, and on rare occasion it can actually make matters worse by rendering Ubuntu unbootable.


• Create a proper /etc/grub.d/40_custom entry for Windows. The one in your original question might work on a BIOS-based system, but under EFI, it will fail. You'd want something that looks more like this:

.

menuentry "Windows" {

    insmod part_gpt

    insmod chain

    set root='(hd0,gpt1)'

    chainloader /EFI/Microsoft/Boot/bootmgfw.efi

}

Note that this exact 40_custom entry doesn't always work; you may need to tweak it for your system. (What works on one computer often fails miserably on another.)