DIAGNOSIS This is almost always because the water reservoir isn't seated correctly or the machine thinks it's empty. The beeping is a 'no water' alert.
FIX First, power the unit off at the button. Lift off the entire top cover. Take out the clear plastic water reservoir, check that it's filled to the MAX line with cold water, and then place it back in. You need to press down firmly until you hear and feel a distinct 'click' on both sides—it locks into place. Close the top cover and press the Power button again. It should stop beeping and the 'Add Water' light should go out.
IF THAT DIDN'T WORK Check the float inside the reservoir well. Make sure it's not stuck in the up position. Gently wiggle it to free it. Also, ensure the ice basket is fully clicked into its slot; if it's not, the machine might not start a cycle.
HEADS UP Always use cold tap water to fill it, especially for the first run. Using warm or hot water can confuse the sensors and delay the initial cycle.