简单的Xcode Hello World显示控件然后它们立即消失

I haven't done any iOS development for like a year. I updated OS to OS X 10.11.5 on my MacBook Pro. I updated Xcode to v7.3 I did Xcode > New project, single view. I set target OS to v7.1 because I'm testing on an iPhone4. I used Storyboard to drag a Label onto the screen and set to Hello World. But when I run simulator iPhone4S, it displays label then it disappears. When I run on actual iPhone4, it displays nothing (all white).I haven't done any iOS development for like a y