Marvin has a number of options for the display of implicit and explicit hydrogens. Because Marvin is chemically intelligent, it will automatically add hydrogens as necessary within the structure. They are called implicit hydrogen atoms, are always displayed without bonds and based on the options set in the View menu. In case of Ball & Stick and Spacefill modes, the impilcit hydrogen atoms are never displayed.
To view all hydrogen atoms explicitly, displayed as atoms with bonds connected to neighbors, chose Structure > Add > Explicit H Atoms. The Structure > Remove > Explicit H atoms will remove every explicitly drawn hydrogen from your structure.