Have you tried running check disk on it? I know it might be too trivial of a suggestion, but I have seen it do many wondrous things, and it doesn't hurt to try
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Open "My Computer", right click on the drive and go to properties, then go to the tools tab and click on the "Check now" button under "Error-Checking". Select both check boxes and hit start.
Sorry if I assumed you didn't know that, I just wanted to do it all in one post.
If that does nothing, then post back here and I have an alternate suggestion.
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