Ok i need severe help

I flashed bios onto my new x3 modded xbox and then it gave me a dashboard to start off with. i decided to put an avalaunch dash on my xbox but before i did i tryed to put xbmc on my xbox (It was an optional download so i got it) but before it downloaded all of the required data i shut it off to put on my avalunch dashboard and when i went into the dash at the top there was a xbox medi center option so i could not click on it. so i decided to delte that dashboard to get to the old one but it would not let me it only leaves me with the ms dash. What do i do i want an avalaunch dash but how do i get it???