Check the clip cord to the power supply and make sure it is seated properly in the grooves at the top of the machine. A loose clip cord results in sporadic or no power to the machine.
Verify that the power supply is plugged in to a functioning outlet and that the foot pedal is correctly attached to the power supply.
Check that the armature bar is moving freely without touching the front coil. Adjust the contact screw so that the bar moves freely.
Check the needle position. If a needle is set out too far with a thick ink, the ink will have trouble entering the skin. Adjust the needle position so ink moves freely.