I actually had a similar thing happen to me yesterday. Was messaging someone, went back to the homescreen and no icons were showing. Thought "hmm that's weird, I'll give it a reboot". Unfortunately it didn't reboot, it tried and then booted into Recovery. Rebooting from Recovery didn't work, wiping Cache didn't work, the phone just magically stopped booting!
So I fired up Odin and reflashed the stock Australian rom (not the carrier version, those are annoying) and it worked! Rebooted fine and I didn't lose any data (except root, which I added again). I wonder if it's a root bug?
SGS4: Stock ROM, rooted w/ CF-Root
HP Touchpad: CM9 tenderloin 28-Apr-13