I had installed wd i tb harddrive instead of old 500gb with service pack 3. now it all works fine. but for last 2-3 days it suddenly shows bluescreen warning for a second and then reboots and than works fine. sometimes for 4-5 hours nothing happens. It happens so fast that I can't read the blue screen warning. it appears and pc reboots. and then everything works fine. there is no problem. I had service pack 2 first and it never happened . the new hard drive is working fine too. My antivirus is secure too. Is there a security feature in service pack 3 which makes it does so or anything else. how can I identify the problem