Notification Problems

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http://androidforums.com – I own a Samsung Galaxy 111. A fat white arrow with a black minus sign recently appeared in the top left hand corner of the screen. I've read that this means that the notifications have been turned off and that if I turn them on it will go away. I can't seem to locate where to turn them on. This problem seems to have coincided (I think, not 100% sure) with no longer being able to hear when text messages come in. Going into settings / sound / default notifications is not working. Would love some help (General)