Sorry, I can't answer your question, but where did you find the hidden numeric keypad? I can't find it on my Inspiron 5030!
Studio XPS 1645 does NOT have a way to turn numlock on.
If you run quickset, you'll notice that there's nothing about function keys or keyboard, other than the backlight.
Is there a "hidden" num pad? How did you find it?
If you press (Fn) and the corresponding key, you get:
(J)=1 (K)=2 (L)=3 (M)=0 (U)=4 (I)=5 (O)=6 (P)=* (= -
For whatever it's worth.