Cursor & Cell not Moving?

In my excel spreadsheet I used to be able to enter a number then use my arrow key to move one cell to the right and then enter the next number.

Now when I enter a number in a hightlighted cell and use the arrow key to move one cell to the right the cell does not move my page shifts to the right but the highlighted cell stays in the same spot.

I must of hit some kind of key combination to cause this. Does anyone know how to fix this?

Thanks