Nothing to do with RAM.
The link you were given describes what you've already done!
When you've done what bugzz said (which you have), then the usual cause is a glitch that caused the HDD to write in the wrong place (like the header information).
Either this is a bad drive (unlikely) or a power spike coming from the mains or your PSU.
Anyway, it's rendered your HDD unuseable. It should be detected by a low level utility like FDISK. But that seems to be academic now as you've posted your solution. Perhaps you could mark this thread as solved.
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Posting Virtuoso
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since Aug 2007