Is the phone talking to you? If so, you've inadvertently turned on talkback.
If it is talking to you, try this to unlock: Wait until the phone isn't talking. Tap the home screen twice, quickly. If the phone starts talking again, wait until it shuts up, then swipe with two fingers. If that works, the following should help you turn talkback off:
If you have Lighflow installed and are using the stock Touchwiz Launcher, that's likely the reason. LF and TW don't get along. To start, uninstall Lightflow, but that might not eliminate the problem.
Talkback is hard to turn off, because it affects how the system responds to touches. A single tap just reads what it is you're tapping on. To actually tap a button, you need to wait until the phone shuts up, then single tap it to set the focus, and then double tap the button or item you want to tap. In order to scroll a screen, you need to use two fingers. So, using double taps and two finger scrolls, and lots of patience, navigate to Settings / Accessibility and turn Talkback off.
If Lightflow was the trigger, and you want to keep using it, try using an alternate launcher. I like Nova better than TW in most respects anyway.