First thing I would try is opening it from a different user account.
If you don't have one then nows the time to make it (system prefs./accounts).
If that doesn't work, try going to: hard drive/user/music/itunes
and put the itunes music library file in the trash (don't empty it) If it doesn't work then just put the file back where it came from.
If that doesnt work then try putting the iTunes preferences in the trash and try launching it again. You can find the pref. file in:
Dolomite, the tough black mineral that won't cop out when there's heat all about.