QuickTime as default media player

Hello,
A helpful window popped up asked me to set Windows Media Player as default. A line on the box assured me that I could undo the default if desired later.
Foolish me. I clicked the default for Windows Media Player. Now:
!. I can't find any way to undo the default.
2. Since defaulting to windows Media Player, I cannot use iTunes (IPod). I was told to uninstall QuickTime. I did that. Then, install QuickTime. Everything was to work. I can pull up QuickTime but I cannot not pull up iTunes. the iTunes libraries are in their proper files but I always get a message that iTunes is experiencing a problem. I click for all of these to go to Microsoft. They eventually respond with a message but following it's directions solves nothing.
Probably my fault.
Got any experience with this?