need someone to explain step by step how to previes partial file. to save getting wrong movie

Well, actually LW has a preview function (right-click on the file and choose preview) but that might sometimes not work.
Another way would be to download the VLC player (it's free, has built-in codecs and is one of the most stable and most recommended players) here:
http://www.videolan.org/vlc/

If you want to preview a file with it, just open the player, go to file (left upper corner), choose open file, locate the file (should be in your Incomplete folder) and play it..........

And please, do not double post here in the forums, it's against the forum rules....

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