I tried creating a new project (once this problem starts happening) and creating just a solid with a bunch of effects on it and trying to render that.. it hangs just the same.. with no imported media and just a solid and some effects.
it looks like even when I quit After Effects, a couple of the AfterFX.exe processes continue to remain running and I have to kill them manually.
I've noticed, if I go into settings and turn off MP, then go kill those extra processes, and then turn it back on it'll load fresh executions of the render nodes and it'll render just fine... then I go back to my problem project and it does the same again..
so once the problem starts, it's there until processes are re-started. it MAY be a corrupt video file, but other times I render it's been fine. even this morning I got ONE good render, and then this problem reared its head once again.