Prove that D4 (Dihedral group) cannot be expressed as an internal direct product of two proper subgroups.

I know that the only two possible subgroups would be the subgroups of order 4 and 2. I am thinking since D4 is not commutative I can get a contradicition this way, but I am not sure how to do it. (Crying) Any help would be welcomed(Evilgrin)