Vista - All programs opening up in Windows Media Center

I am using Vista Home Premium on a Dell Notebook and it has been working
well for me, until now...
I did something and now all programs that I usually run only default to
Media Center, which is not where I need to be. Thought that I could restore
to a previous date, but the restore file also takes me to windows Media
Center. Even booting up to safe mode fails.

Can somebody please help out here and let me know what I can do to get
things back to normal. I am not keen to reformat, if I can avoid that step.

Thanks
"What the Heck"