#8 Player failure to operate

I am running mac os X version 10.6.8. I used the umplayer to look at a few stored movies and it worked very well. I went back to look at the same movies a few seconds later and now the player does not work. The sound plays as it did before but instead of a picture on the player all I am getting is the logo. This is happening even with the movies that played perfectly a few seconds before. I have tried to reset preferences to their original state, re loaded the player a few times and there has been no improvement to the situation. Any suggestions?