The unit may be stuck in either shutdown mode or single user linux mode. Try removing the front over and pressing and then immediately releasing the reset button. Note that if the reset button is held in for 1 or more secs it can result in the unit shutting down to single user mode or completely shutting down. Once in this state, power cycling the unit will not necessary get it to boot normally again. The only known way to clear it is the quickly press and release the reset button.