I have a 23” Cinema Display that died in the same sudden manner. I troubleshooted it and found that the power supply was bad. web searching revels that is a very common problem with these old Cinema Display power supplies.
the cord from the power supply to the display (with the oval plug) has only 3 wires (despite there being many more than 3 contacts inside the plug)—red: +24.5v, black: DC negative, and gray. gray is the “sense” wire that tells the display that the apple power supply being connected is of proper wattage. we can leave that wire not connected.
the 23” uses a 90 watt supply so I used a 24v 4 amp generic power brick and connected the red and black wires to the corresponding outputs of the power brick. plugged in the brick, connected the display to my MacBook, and the display lit right up.
your 30” display uses a 150 watt power supply, the safest route would be to buy a used Apple 150 watt PS, which I see on ebay for about $100. but if it were me, I would buy a 24v generic power brick rated at 7 amps or higher and roll your own.
disclaimer: since the apple PS’s are rated at 24.5 v there’s always a chance there might be a problem down the road. I chose to not buy a used Apple PS because there is no telling how long a used one will last, and they aren’t cheap. but this decision is mine alone and YMMV.
the bottom line in my mind, based on web research, is that the problem with suddenly-dead cinema displays is most likely due to bad power supplies, not the electronics inside the display.