Is it ok to uninstall Windows Media Player and download a new one?

I just bought my laptop, took to degrade it from vista to windows XP. Then when i wanted to use my windows media player, they asked me to update it. So, despite my dad's constant advice to never click on the update on, i still did. Everything went well until i tried to restart wmp. They told me that my windows XP or something like that ain't valid. When i asked the person who degraded my laptop, he said it was the original thing. So i can't use my wmp and had to stick to quicktime but i can't play songs in a play list... so should i uninstall it and download it again? Is there even a site to download it? Will it be original? Or is there a better solution? Maybe you can also recommend me better soft wares than wmp that can play songs, play lists, burn, sync with mp3, and play movies/videos