Multiple cell selection
 

We just got Excel 2007, and every once in a while, when I go to pick a cell
to enter info, alot of time it will automatically also highlight the cell
under the cell I picked, and in some cases, it will highlight 2 cells under
my selection. Is there a reason why its doing this? I'm trying to drag a
formula down a column instead of retyping everything, and I cant grip the
bottom right hand corner because of this glitch.

Thanks!