DIAGNOSIS The control board is receiving power (hence the beep) but is locked up, usually from a brief voltage spike or a child lock feature being activated.
FIX Perform a hard reset. Unplug the unit from the wall outlet. Wait a full 60 seconds. While it's unplugged, press and hold the Power button on the control panel for 5 seconds to discharge any residual capacitance. Plug it directly back into the wall outlet (not a power strip). This reboots the logic board.
IF THAT DIDN'T WORK Check for a 'Control Lock' or 'Key Lock' function. On some models, holding the Timer button for 3 seconds locks the panel to prevent accidental presses. Try holding Timer or each button for 3-5 seconds to see if a lock icon appears/disappears.
HEADS UP If the hard reset works but the problem recurs, plug the unit into a different circuit. Consistent lock-ups can be caused by a weak or noisy power supply from that particular outlet or an overloaded circuit.