My screen won't rotate! Thre is a check mark next to lock rotation in the general settings and I can't get the check mark to go away!

-----URGENTLY SEEKING HELP------

Whenever I turn my iPad for a "horizontal" view, it stays locked onto the vertical view, furthermore whenever I turn on my iPad it is locked into an upside down view. I checked under my "General Settings" and discovered the "lock rotation" has been checked, however I can not get the check mark to disappear! Please HELP!