The best way to restart a download that has stopped is this:

Right-click the file (in download window)...search...search for keyword

If this doesn't work after several attempts (at different times), then you may want to try to find another copy of the file.

Good Luck

P.S. You can try to vary your searches to find a file with more sources, i.e. I get better results by searching the song name rather than the artist.