You didn't, by any chance, install P4 directly over P3 did you? I understand that this is one of the main reasons for having P4 crash on start-up. At this point it may be worth while to save all your work (yes, I said "save your work" ;-p), de-install P4, remove the directories and make a clean install. There have been a couple of instances I've seen that solves these problems. Something has been nailed really bad so it's time for drastic action.