Liza,
You need to test the DC voltage going from the power center to the cell. Should be about 40 Volts DC. You test between the Red and Black wires going to the cell..
If you have no voltage, or very low voltage, unplug the cell from the power center.. If the voltage goes back up to 40 VDC, then the cell is bad.. If the voltage stays low, then most likely the power center is bad.
Thanks,
Jim R.