An issue some folks have been having with the 23-inch Apple Cinema Display concerns the screen shutting off and displaying a pulsing LED status that alternates between long and short pulses. This pulsing indicates a problem with the voltage the unit is getting from its power supply, so the issue is likely not a problem with the screen itself.
Affected users have found that the problem seems to be with how the inverter board on the display is handling the power sent to it by the included 90-watt power supply. Apparently a grounding issue with the power supply is resulting in a drop in voltage that results in the unit shutting down. As a result there are several options available:
Repair the unit
Apple will repair the inverter board with a working one; however, this may cost a few hundred dollars if you do not have a warranty for the system.
Purchase a higher-wattage power supply
Apple provides a 90-watt power supply with the display, but people have found that using the 150-watt supply that is issued with the 30-inch Cinema Display will prevent the error from occurring. Using a higher-wattage supply will not harm the 23-inch display, but it will have enough capability to meet the power demands of the systems that are having this grounding error. A 150-watt power supply can be purchased online at outlets such as dvwarehouse or eBay, among others.
Bypass the display's ground
A number of people who are unwilling to spend about $120 on a new power supply have also addressed the issue by blocking the grounding pin on their power supply (thanks to a suggestion by Apple discussion user "jakobeon"). To do this, they have covered the center grounding pin on the display's power connector with a piece of either paper or plastic, and then gently inserted the connector to its slot on the power supply.
While the grounding from the display to the power supply is less important than the grounding of the power supply to the wall, there is still some potential risk of electrical damage that can result from blocking a grounding connector. Nevertheless, the probability of damage is relatively low, and since the initial problem is from a grounding fault in the first place this solution should bypass the problem and get things working again.