Have some trouble. (change default player)

So I installed Nero today, which included Neromix. When i started to play my video files, it played on the Neromix player, and not Windows Media or Quicktime, and I do not want it to play on Neromix.
Now I have unistalled Neromix, Nero all together, and I have also installed limewire a couple of times, and now my files will not play on anything. Is there anyway I can change the standard player for my video files, or make it so that my avi, mpeg, mpg ect. files play on Windows media, and my mp4s play on Quicktime?

Open WMP, click on the little arrow next to 'minimise'. From the dropdown menu click tools > options. click the File Types tab. Tick all of the file types that you want WMP to open > apply > ok.

If that doesn't work, open LW's saved folder by highlighting a file & clicking Explore. Once you're inside the saved folder, right click on a file > open with > choose program. Choose the player that you want to use from the list & tick the box to always use the selected program to open files of this type > ok.
Same thing for your mp4s...choose QuickTime from the list of players