Its hard to guess with very little facts, but the most common reason for this (apart from a damaged Poser) is memory related. How much (real) RAM do you have, how much virtual and how much is for Poser? You should never give Poser the entire memory, try to leave at least 5-10 MB free for the system to breath. Poser will trigger some system services on startup (QuickTime, to mention just the biggest one), and if there is nothing left at all (while Poser is still starting up) it could start to throw bombs.