For Macintosh
Save your work and close Illustrator. Open the Finder and then go to Go > Home > Preferences. Look for a folder called Adobe Illustrator settings. In the folder is a file called Adobe Illustrator Prefs. Drag this file to the trash. Empty the trash and restart Illustrator. Reset any custom preferences you want, and when you close Illustrator the preferences file will be regenerated.
You can also reset Illustrator’s preferences by holding down Shift + Command + Option + Control while opening the program. If you will get a dialog asking if you want to delete the settings folder, say yes. Restart Illustrator. Reset any custom preferences you want, and when you close Illustrator the preferences file will be regenerated.
For Windows
Save your work and close Illustrator. Double click on My Computer on your desktop and open C:>Documents and Settings > User >Application Data > Adobe > Adobe Illustrator Settings. Inside this folder is a file called AIPrefs. Drag this file to the trash, and restart Illustrator. Reset any custom preferences you want, and when you close Illustrator the preferences file will be regenerated.
You can also reset Illustrator’s preferences by holding down Shift + Control + Alt while launching the program. If you get a dialog asking if you want to delete the Adobe Illustrator settings folder, click yes to proceed. Restart Illustrator. Reset any custom preferences you want, and when you close Illustrator the preferences file will be regenerated.
