When you are exporting a song there are options to determine what portion of the song gets exported - one option is to go from the "start" marker to the "end" marker. That is the option I use - it is possible that you are not selecting all or any part of the song? When you look at the properties of the wav / mp3 file you created is it the appropriate size? MP3 files should be about 2mb per minute, and wav files about 10 mb per minute. If you are creating a file of the right size and windows media player won't play it, I would try another media player or even try to import it back into Studio One.
I hope this helps.
