Right, I've got a problem and I really need your help. I bought a Mac Pro 4,1 computer in late 2009 with a 24" Apple Cinema Display monitor. In 2013, I was playing a graphically intensive video game and without warning the screen went black. I shut off the computer at the wall, but the screen didn't light up when I booted it back up. I retried this many times, but the screen never turned on with the computer. I didn't know if the problem was with the GPU, or monitor, or some other component. Without visual accompaniment, I navigated to the Desktop and used the keyboard shortcut to reduce the brightness, and then shut off the computer. With the brightness at it's lowest setting, the screen lit up when I powered on the computer. However, another problem, the screen blinks rapidly and then shuts down, or stays on. On average,I have to power on the computer roughly 5-20 times before the screen stays on. I found that I couldn't have the brightness above 10/15 increments after that day. A few months later, it dropped to 6/15, then 3/15, and now it's on the lowest brightness setting. I've postponed the problem until now, but it has to be sorted, as the experience is hardly useable. Presuming the issue was with the GPU, I purchased a Nvidia GTX 680 recently, but the brightness issue remains. The fans on the card spin into action, and the appropriate software drivers are installed, and the power cables are plugged in, but I get no response from the monitor. This suggests to me that the problem is the monitor. The monitor is only able to power the default GPU on the lowest brightness setting, and can't power the GTX 680 at all. So, I don't know where to go from here. I want to repair the Cinema Display monitor, but don't know how to do that, or if it's possible. It was dan extremely expensive monitor when purchased, and in my opinion is still relatively young (seven years). I don't know the anatomy of a computer monitor or how it works. Is there some part inside that can be replaced? Could the problem be the power unit inside the Mac Pro? Do you have any suggestions as to how to further troubleshoot or solve this issue? As it stands, I can barely see what I'm doing on the computer.