When it asks you to press the numeric keypad, before the game begins, enter one of these codes.
8,1,6,4,7,5,2,3,9? - Gives you a bronze hammer with 100 coins
9,6,5,8,1,3,4,7,2? - Gives you a sliver hammer with 100 coins (starts at level 11)
7,2,6,5,3,8,9,4,1? - Gives the choice to start at whatever level you want, a ray gun with 50 ammo, 6 ice hearts, and 999 coins.
I hacked this game also, check it out here!