[ubuntu] system monitor shows single core

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http://ubuntuforums.org – Hi !! I have system with Pentium D dual core processor. Recently my conky & system monitor showing that only one processor core is working instead of two. Is this normal software problem or wrong Bios setting ? or my second core processor is not working? Is it possible for system with dual processor to work even if one of two processor get damaged? Recently I have changed my old 80 GB hdd with 500GB. Since it never get detected in first boot I have changed some of BIOS settings but till it doesn't get detected in first boot. I have restart twice to boot on hdd. Why this is so ? Is there (Hardware)