Received message that windows XP needed to shutdown due to major problem (undefined in understandable terms). I have tried to reboot with the whole process going through to windows booting up screen...power light green and ok, info transfer going to windows stuck on yellow. I've tried to start up in safe mode. Nothing. I can start up but will not go into windows operational menu or start up menu. I might add that I was in the lengthy process of Speed Disk defrag.......Hmmmm. Thanks for any light you can shed.