Borealis, you're not alone. I ran BitDefender on my HP and it ran fine. However, when I ran BitDefender PRO, it F***ed up my computer and I had a hell of a time correcting the problem. It wouldn't re-boot. I finally was able to run it in "safe mode" (after 3 tries at this) and make my way to "System Restore" and "turn back" my system to an earlier date. By the way I have an HP 7905, WinXP Home Edition , P4 1.6 Ghtz and 512 MB RAM.