First it ignored the “slide to unlock” slide. No motion would make it go. I found a workaround: make the slide motion anywho and then press the on button.
But eventually, Safari began to crash at odd times. The other apps would crash. Things were getting worse. Even sliding between photos would cause the app to abort and I’d be thrown back to the home screen.
A reset seems to have fixed it all. Just hold down the on/off button at the top right of the iPhone at the same time you hold down the home button at the bottom center for about three seconds. Eventually you see the Apple logo and then shortly after you are rebooted and reset. For me the problems were all cleared up.