dsp 964 ds3p 3.3 mb

all of a sudden when i shut down win xp (sp3) the power light on my antec case remains on.

i've checked the obvious, suspend / hibernation, etc., are all turned off, and i've checked in bios and lan wake-up etc., is also turned off.

this is not such a big deal since i can easily access the mains switch on the back of the case, but i'm really curious as to what's causing this behaviour.