How to restore missing dual boot menu in latest Windows 10 build

I have just installed Build 9879 onto a second SSD, thinking I would be able to dual boot with Windows 8.1 on the first SSD.  No dual boot menu comes up.  I tried the steps in this article, and only Windows Technical Preview comes up.  I've tried going into the BIOS and booting from the first SSD, but Windows TP loads up. 

Under Disk Management, I see the second SSD where Windows TP is installed as 'Boot, Page File, Crash Dump, Primary Partition'.  The first SSD where Windows 8.1 is installed shows 'System, Active, Primary Partition'.  It seems the boot loader files have been deleted on the Windows 8.1 drive. 

How can I get this system to dual boot?

Try this:

Press Windows key + X

Click Command Prompt (Admin)

At the command prompt, type the following:

bcdedit /set {bootmgr} displaybootmenu yes

Hit Enter on your keyboard

Type: exit

Restart and see if it shows up.

Andre, tried that, it says operation successfully completed, rebooted and still no dual boot menu.  Ran msconfig and under Boot tab, only Windows TP shows up. 

What I can't understand is when I select to boot from the SSD that Windows 8.1 is installed from the BIOS, it still loads up into Windows TP.  It's as if the boot loader files on that drive have been wiped out by the install of build 9879, even on a second SSD. 

Microsoft, can you shed any light?

You could try using EasyBCD to add a boot entry.

Download EasyBCD 1.7.2 - NeoSmart Technologies

Fixed it!  Writing this from Windows 8.1.  Thanks Andre for the suggestion of EasyBCD, saw it on another post and installed it, added the entry, and that got me the dual boot menu.

Ah, the pleasures of testing beta software. 

Thanks for your assistance.

I understand that this is a build 9860 article, but:

I use

bcdedit /set {bootmgr} displaybootmenu yes

But after about every 2-3 reboots build 9879 reverts this option: an issue so persistent I actually created a desktop shortcut for the above command. Ideas?

The reason being that I have a dual-boot configuration, Windows 7 and Windows Technical Preview, and I find it highly inefficient to have the boot options displayed after Windows 8/8.1/10 is fully loaded and then reboot the system to load Windows 7 in the event that I do choose Windows 7. (As an added bonus, my machine has two extra screens in the BIOS after the manufacturer logo. You can probably imagine the time consumption.)

By the way, I actually found the bcdedit command in a Safe Mode KB article specifically for Windows 8.

Try this:

Press Windows key + X

Click Command Prompt (Admin)

At the command prompt, type the following:

bcdedit /set {bootmgr} displaybootmenu yes

Hit Enter on your keyboard

Type: exit

Restart and see if it shows up.

I am using Build 9926.

When I attempt this command I get this response:

"The element data type specified is not recognized or does not apply to the specified entry.

Element not found."

Len Goodwin

When I attempt work around 2 I do not see alternate OS settings.

Len Goodwin

This  does not appear to work. Neither of the suggested workarounds produce a positive result.

BCDEDIT does not recognize the element bootmanager, and workaround 2 does not display both OS, only Win 10 TP.

I can use EasyBCD, but don't know what to add, since when I call up bcdedit /v it only gives me the content of the c: boot manager, not the version on disk d: (which is the Win 8.1 install).

Any other ideas? Should I wipe the drive on which I installed 10 TP, or will that leave we without a boot manager, requiring a fresh install?

Thanks,

Len Goodwin