Every time you install a new player, you are asked whether you want that player to be your default player. Of course the makers of that player want you to use it for all your files, so by default (if you just select OK over and over during installation) you will opt to make the new player your default player for all file types.

Try this: right-click on one of your files and select 'properties'. You can choose which program you want to open that type of file.

Good Luck