On many laptops, you have to press and hold the "Fn" key then press the corresponding F key (F1-F12) that releases then numlock. This key is labeled "Number Lock", "NumLk", or with a picture of a keypad.
Since I don't know specifically what Vaio you're using, that's about all the help I can provide. If your laptop doesn't have a "Fn" key, consult your user's manual. It will tell you how to turn on and off the number lock or keypad function.
And if you're really still stuck after all of that, try this: Some laptops will respond to an external keyboard's numlock key being pressed. Plug one in, press the numlock, unplug it.