MadMonkey: The only thing that quickly comes to mind is some sort of device hooked to the PC is causing it to hang.

As a side note, I just troubleshot a laptop which about every 2 of 3 bootup would hang as it was initializing it. Found the problem to be a newer USB thumb drive that he kept attached to the laptop. He actually had 2 attached - the older one never caused a problem, but with the newer one attached, the bootup process would just hang. Now he just waits until windows boots up before plugging it in.... and remembering to remove it before next bootup.