My old PC took a dump. I've replaced it with a new Dell XPS 8920 running Windows 10.

I've installed the SSD drive from my old system which has Ubuntu 16.04 installed.

Device Manager in Win10 doesn't see the Linux SSD but a partition manager identifies it just fine.

I'd like to dual boot from the separate existing SSDs but I'm having problems accessing the UEFI BIOS.

It seems the only way to access the boot devices is through Win10 Restart Advanced options while running Win10. Hitting F2 (or any other key) during POST doesn't catch.

Has anyone been able to add an SSD already running Ubuntu 16.04 to another computer running Win10 and been able to change to a dual boot?

Help me get back to Ubuntu, please :-) 

You have to get it to "catch". With UEFI, you need to add an entry to the NVRAM - Linux installers do this for you.
Does that also mean you can't get a liveUSB to boot ?.

Syg00,

You said I'd need 'an entry to the NVRAM'.
How would I go about that?

Yes, a Live DVD would catch, I'm exploring just what UEFI and Boot Options means.
There are so many conflicting answers.

Thanks,

John

If you can boot into the live-whatever, the easiest way to fix this is to chroot into the SSD Ubuntu, and do a grub-install to (presumably) /dev/sdb. Then an update-grub would be a good idea. This will create all you need. There are good Ubuntu articles online.
You could, of course, simply install to sda and replace the Win10 loader - don't know how you feel about that.

Edit: forgot to mention. If you do install to /dev/sdb, you will have to find a way to display the boot list else you will never get to it. Typically F9/F10 immediately after POST.

Try spamming other keys at bootup. F12, ESC, what have you. ESC on my hp stream 11, F12 in a gateway desktop, long ago, DEL, SPACE, and others were the magic key.

http://www.dell.com/support/article/...indows?lang=EN

Seems like F2 for that system is the key. Spam it though until you're in the setup. Timing a single tap once Dell Logo and keyboard LEDs blink, is much harder to do. Perhaps there's an option that helps enable that button that defaults to off, or other doesn't really save despite F10 to save + exit or whatever applies. One of the quirks of boot USB first for the current desktop. Will do it first time out, will not save that priority for future boots. And of course check for bios/uefi updates for your motherboard, which might make things behave more expectedly.

Extra info.

If you want to try to let windows boot to linux. This also assumes that you have a uefi install. https://askubuntu.com/questions/6244...ows-bootloader