Problem in Windows 8 Navigation Buton

I am having Dell Insprion 15 – Windows 8. While am working today the navigation buttons are changed in to special characters like boxes in IE, Start screen. Especially in start screen, if we right click the mouse button, a small slide will from bottom and there will be a circle and “all apps” beneth the circle. instead of circle symbol it comes 3 boxes. Even in the check boxes, instead of check mark, boxes are appearing. Can any one help me out of this please.