Panda TruPrevent is probably your problem. Try starting up in Safe Mode. Safe mode is a way of starting up your comp where only the absolute necessary processes are started up.
As your starting up, continually Press F8 until you get a boot screen, with choices of how you start up. Select start up in safe mode, then choose from the list of operating systems. If your comp starts up fine, then Panda is the problem. In Safe Mode you are still allowed to uninstall programs.
Yesterday I Bought Panda TruPrevent (I refunded you'll see why) and I installed and registered .I restarted my computer and went to the welcome screen (XP) and I put pass word and it said welcome like usual. And i got a blue boot screen of death saying the system is shut down. A little help here???