Problem:

Installed Windows 10, installed steam, xbox button on controller doesn't open up Big Picture any more

Solution:

Need to disable DVR setting in the xbox application that comes with win10.

Can either login into the xbox app and disable the DVR option under settings, or if you can't login for some reason, you can press the windows key and g in any program, and select "this is a game", then turn off the dvr setting there.