Reset all preferences to default settings
Resetting preferences can be helpful if you are having problems with the application.

Do one of the following:
Press and hold Alt+Control+Shift (Windows) or Option+Command+Shift (Mac OS) as you start Illustrator. Your current settings are deleted.
Remove or rename the AIPrefs file (Windows) or Adobe Illustrator Prefs file (Mac OS). New preferences files are created the next time you start Illustrator.
Note: It is safe to remove the entire Adobe Illustrator CS4 Settings folder. This folder contains various preferences that can be regenerated.