I woke up this morning and my phone was working as usual. After a few minutes' random surfing and texting, nothing out of the ordinary, it 'froze,' as it tends to do occasionally, and I could tell it was about to reset itself (happens once or twice a week, a bit annoying but nothing out of the ordinary). It did reset, the robotic "Droid" voice came through, and the standard splash screen showed up (I guess as a new user I can't post an image to this but it's the go-to red 'eye'-like thing with the pulsating red/white junk). Normal so far, but it wouldn't boot past this stage. After about 1 minute it reset itself again and returned to this phase, and so on and so forth. It's been doing this about 20 minutes now, hinging on the main splash image and then resetting.
Battery is (was 20 minutes ago anyway) fully charged, phone isn't overheated, stock model, no crazy updates or installs. It's been fully functional until just now. I can get to the options to factory reset everything but haven't backed up most of my info in a couple of months; would prefer not to erase everything unless totally necessary.