Who do I fix boot device not found(3FO)

It sounds like you might've corrupted both OSes on your hard drive when you tried to install Ubuntu. I believe that when Ubuntu is installed in a dual-boot setup, it "scoots" Windows over a little bit on the hard drive and slaps itself down on the half that's left. My guess is that it was in the middle of this process when your battery went out, and, as a result, both bootable OSes are now unusable. Try making a bootable Windows USB (How to Create a USB boot drive for Windows 10 - iFixit Repair Guide)and see if you can boot from that. Or you could also try booting from a Linux Live USB. I'm sure you're aware of how to do this since you were installing Ubuntu, but here's the guide for that (Install Ubuntu desktop). If you boot from the Ubuntu Live USB, go into "Try Ubuntu" and see if you can get any of your data back. My guess is that all your data got corrupted with Windows, but maybe you got lucky and some of it is retrievable. I just hope you had a current backup :). Just make sure you plug your computer in before you try that again (hey, that rhymed!) Let me know how it goes!