There are at least two possible causes of your problem:
- You've installed Ubuntu in EFI mode but the GRUB configuration tool has failed to identify Windows, and so is booting through GRUB but with a short timeout and a hidden menu.
- You've installed Ubuntu in BIOS mode, which means that it can't boot Windows (which is in EFI mode), and so GRUB is using a short timeout and a hidden menu.
If you're booting in EFI mode, this might be a bit easier to fix, since you should be able to run Boot Repair from your current Ubuntu and it should be fixed. To determine if you're in EFI mode, look for a directory called
/sys/firmware/efi. If it's present, you're booting in EFI mode; but if it's absent, you're probably booting in BIOS mode.
If you're booting in BIOS mode, you can fix the problem by installing an EFI-mode boot loader for Linux. You can do this in any of several ways, but two relatively easy ones are:
- Boot a live CD-R or USB flash drive in EFI mode and run Boot Repair. This should get GRUB up and running with Windows detected. The trick is forcing an EFI-mode boot of a live CD. You may need to play with your firmware's boot options. Typically, hitting a function key (which one varies) produces a boot menu, and you should select the one for your live CD that mentions "EFI" or "UEFI."
- Download the CD-R or USB flash drive image of my rEFInd boot manager and prepare a medium with it. You should then be able to boot to it. If rEFInd lets you boot both Windows and Linux, boot to Linux, mount your EFI System Partition (ESP) to
/boot/efi, and install the Debian-package version of rEFInd. You'll then use rEFInd to select your OS on subsequent boots.
If one of these fails, try the other one. If you continue to have problems, post back with the URL that Boot Repair provides; this will give us detailed information on your system's configuration.