The easiest way to tell if your device is working is to look for the bubbles rising off the electrodes at each end of the device. The negative end (black) also called the cathode, should have approximately twice as many bubbles forming as at the (red) anode end. If no bubbles are forming, check that the power supply is on, in run mode, and that all connections are secure. If bubbles are forming, then current is running through the system. But remember however, that proper buffer concentration and age greatly affect the elctrophoresis process. If samples are not running properly, then the most likely problem is poor buffer formulation.