help me please

i.ve been very happy with bsplayer. it plays good with any kind of movies i downloaded. But, when i downloaded the nero 6 demo version, nero showtime became the player for all of the movies and i dont know why. Unlike bs player, it cannot recognize all of the movies especially divx movies. And when i tried to play it with bs player it does play good as weel. What could have happened? How can i make my bsplayer the initial player again without removing nero 6.
please help me with it. thanks