If you are trying to play with with WMP, there is a known bug with WMP & LW. Did you update LW recently?
You could always try another player. If it's LW Player that is not previewing properly, then disable it in settings & instead try using your default audio player. Option is bottom left of Tools -> Options -> My Library. Actually disabling it, then re-enabling it might even do the trick. LW's media player can be a bit 'sticky' sometimes.