What boot manager appears? The Windows boot manager? If so, you can try the one of the following methods. (The first one is probably easier.)

Basically, you need to tell the Windows Boot Manager to boot the Windows Boot Loader by default (unless it's already doing this), and then tell the Windows Boot Manager to stop displaying the boot menu.

Please note that if you make a mistake during this process, you may no longer be able to boot into Windows. If this happens, your best bet may be to boot into a Windows disc and use the recovery options there. Especially in the case that you were using Method 2, you can even open a command prompt from the disc and try using BCDEdit again.

Method 1: Control Panel Options

1. Open the Control Panel (Start -> Control Panel)
2. Go to "System and Security"
3. Go to "System"
4. Go to "Advanced System Settings"
5. Go to the "Advanced" tab
6. Under "Startup and Recovery", click "Settings"
7. Under "System Startup" -> "Default operating system", choose something like "Windows 8"
8. Uncheck the option "Time to display list of operating systems". You'll notice that the number of seconds changes to 0.

I found some of the information for Method 1 here: How to change Windows 7 Boot manager options to start the OS automatically?

Method 2: BCDEdit

BCDEdit is a built-in utility in Windows Vista, 7, & 8 that you should also be able to use to solve your problem.

1) Make sure Windows is your default boot entry.

1. In Windows, open a command prompt. (e.g. Hold the Windows key and press R.
2. In the "Run" window that appears, type cmd and press Enter.)
3. In the command prompt, run the command bcdedit to display current boot information. There should be an entry called "Windows Boot Loader" (NOT "Windows Boot Manager"!) followed by a line with "identifier" and a long string of characters enclosed by { }. This string is the GUID (or just "id" or "identifier") of that boot entry.
4. Run the command BCDEdit /default id, where where you replace id with the long identifier of the Windows boot entry, to make that boot loader the default one.

2) Skip the boot menu so you no longer see it.

Use the following BCDEdit command to skip the boot menu so you don't see it: bcdedit /timeout 0. In this command, 0 is actually the number of seconds the Windows to display the boot selection screen.

I found some of the information for Method 2 here:

BCDEdit Command-Line Options

Changing the Default Boot Entry

Do not know how your got grub legacy installed to MBR, but you only have UEFI boot and data in MBR will never be used.

Many vendors now modify UEFI to only boot Windows by description. So ubuntu entry does not work. But UEFI also boots hard drive entry as /EFI/Boot/bootx64.efi. So we copy grub into /EFI/Boot and rename it ot bootx64.efi and system will boot from hard drive entry.

From live installer mount the efi partition on hard drive Mount efi partition. check which partition is FAT32 with boot flag. Often sda1 or sda2 but varies.

sudo mount /dev/sda1 /mnt

mkdir only if not already existing, your have this but others may not:

sudo mkdir /mnt/EFI/Boot
sudo cp /mnt/EFI/ubuntu/* /mnt/EFI/Boot

If new folder created, the bootx64.efi will not exist, skip this command

sudo mv /mnt/EFI/Boot/bootx64.efi /mnt/EFI/Boot/bootx64.efi.backup

make grub be hard drive boot entry in UEFI. If not existing, may have to update UEFI also with efibootmgr.

sudo mv /mnt/EFI/Boot/grubx64.efi /mnt/EFI/Boot/bootx64.efi 

Other work arounds:

Dual boot Win 8 / Ubuntu loads only Win

windows 8.1 changes boot order

How do I get my HP laptop to boot into grub from my new efi file?