New Hang at Startup Issue

[Chris Schumann]

I've got a ThinkPad 600X with FC5. After some recent update, if I try to let
the system boot normally, it hangs just before showing the login screen: The
GRUB interface works fine; X starts and shows all the things that load; X
re-starts and shows the solid blue desktop; I can move the cursor with the
mouse, then it locks up dead.

But if I make it start in runlevel 3 (by adding "3" to the kernel
parameters), that's fine, I can log in and do "init 5" and everything is
peachy.

Where should I look for clues on what's going on?

Thanks,
Chris