You could try selecting "/dev/sdb", or "/dev/sdb1".
This SHOULD keep it from messing with your Win10 drive/install.
I've put my boot loader all over the place and it still worked.
Usually, you have to put the boot loader on a partition: sda1/sdb1/sdc1...
sda/sdb/sdc are the actual
physical drives, the device itself, the "1" is the partition where the data is written...
I've installed Ubuntu twice, once on my brothers PC about 3 1/2 years ago, and the video was too new, and I tried 14.04 on mine about 2 years ago, same situation... So I'm really out of practice with Ubuntu...
Which version of Ubuntu did you download? I'll install it in a virtual machine on my PC, so I'm more familiar with the steps for it...
Barracuda
P.S. I keep typing Ubuntu as "Ubunto", then I have to stop and correct my spelling....
