I wouldn't go that far, yet anyway.

Go down this path
HD/Users/YourUserName/Library/Preferences/com.apple.iCal.plist
Move that plist file to your Desktop.
Now open iCal. This will make a new default plist file.
Test it out. Is it better? Back to "normal"?
If so, Trash that file from the Desktop.

If not, try using iCal after logging in under a different user account. If you only have one, make a second one!

And, if step one made things worse, you can put that plist file back where it came from. It will ask you if you want to overwrite the one it just made. You should do this if you changed a bunch of preferences. That will restore your changes.

This approach is trying to ferret out corrupt preferences or other things in your account, if that's the problem. We weren't getting anywhere looking for an answer within iCal.