I'm coming in late to the game here, but from what I've read it seems to me that the best thing to do is back up any important USER-CREATED FILES (photos, documents, music, etc.) - then erase the hard drive and install a fresh system.

Trying to troubleshoot a system that has multiple system folders that (if I recall) were installed by someone else is enough to drive you mad.

Just my 2¢
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