[ubuntu] operating system not found after updates

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http://ubuntuforums.org – Hi, My computer is a Lenovo x120e AMD 64. I have been running Ubuntu 12.04 LTS since April with no significant problems. Today, I installed recommended security updates which is something I do regularly. The system required restart to complete the updates and so I restarted the computer. Upon restart, I now get the error message "Operating System not found". I switched the bios to diagnostic mode and I see where the computer is finding my hard drive, "Fixed Disk: WDC etc." Prior to this problem, my hard disk was operating normally with no loud noises or other indicati (Hardware)