Puzzling 50/50 hang at "Starting Windows"

What's puzzling is that all of a sudden, I need a two-step process to boot normally into 64-bit Windows 7 SP1.

When I first try to boot up normally, I will only get to the "Starting Windows" page, and then it will go no further, no matter how long I wait. But if I then boot into Safe Mode, and while there do NOTHING at all but reboot normally, it works perfectly the next time!

But if I then restart, the whole loop repeats again!

Since before this strange behavior began, I've installed nothing, I've uninstalled nothing, I haven't changed any hardware or software configuration. DSKCHK reports no problems whatsoever on any volume. As far as I can tell with manual investigation, the registry looks fine. Using the Autoruns tool, everything looks exactly correct. Nothing stands out in the boot logs.

And when you consider the fact that I don't change anything while in Safe Mode, this entire scenario makes not even the tiniest bit of logical sense!

Obviously, I can just resign myself to booting twice in a row from now on, because I can then continue to work normally, but this is so weird my curiosity just won't let it go. What the heck's going on here?

Never mind. The problem went away on its own...