Do you have any subscribed calendars? Maybe disconnect your network connections and then try reopening it. If that doesn't work, then find a file named com.apple.iCal.plist in the Preferences folder and drag it to the Desktop before reopening iCal.
Well, if you create a new user account in System Preferences, does it open from there? If it doesn't, then we can quite safely say the problem is a corruption in one of the files on your Home folder.