If you still have the tunes on your hard drive, I can only imagine you must, somehow have moved them. If you right click >open with>iTunes they will again play in iTunes. You have the option in iTunes preferences>advanced>general to add a copy of files thus added to your iTunes folder. You will need to delete the old listing in iTunes. Alternately you could try to open them in iTunes and you should get a browse to find the file option.

I hope this helps.

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