It depends, if it is a fault then powering down then back up it may come back online.
I am now assuming this is in a machine that was working?
If so then I expect you may need someone with the software and is familiar with it to look at it. It is also possible something has either corrupted or cleared the memory too, like a dead battery, if power is turned off and battery bad memory is cleared.
Usually the lights, Power, OK, RUN, and BATT will give you a clue. If Power is not On and you know it has power to it, then the power supply may be bad. The other lights will offer other clues, tell whether each is on, off, or flashing.