Drat! This makes it rather difficult to fix, since the place that you normally go to fix these kinds of problems involves getting into the Settings menu!
I can only suggest rebooting into Recovery mode (with the phone completely off, press and hold the Volume Up and Home and Power buttons simultaneously, and release them all when you see the splash screen) and clearing the cache.
If that doesn't work I don't know what else to suggest besides a Factory Reset. Since the phone is working, you should be able to use the Kies software on your PC to make a backup first.
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