I popped in my old card, disabled Secure Boot, reinstalled the new card, and all is well.  
My XPS 8700 with GeForce 720 works fine.  I then installed a GTX 660 and it would boot straight into Windows 10 where I don't see the Dell logo for me to hit F2 to enter BIOS.  I did tried to just hit F2 continuously during boot up but then it would get stuck at a black screen until I hit ctrl-alt-delete in which it would then boot into Windows.  When I reinstalled the GeForce 720 card it works fine and I can boot into the BIOS or Windows.   Couple of things I've tried:
XPS 8700, GTX 660, unable to boot into BIOS