A few months ago I was reformatting, upon installing windows XP my 1024x740 monitor went very dark, as if the brightness was set on 1%, you could barely make out the odd window or progress bar, I switched it off for half an hour came back and it was fine, plsu my installation had completed.
However, yesterday it happened again, didn't work for a few hours, I had actually started using my old 600x460 (close enough), tried it after about 2 hours of using the old monitor, worked fine.
After about 2 hours use of the new one again, it would flicker slightly, go dark and you could switch it off and on and it'd work again for a while. that happened within about hour periods for the rest of the evening.
Today, it works fine until about 10pm (GMT), it goes dark and does what it did the first time it happened, you can switch it off and back on, it'll come on with the right colours/brightness, for less than a second, then it'll go dark again.
It's a 15' LCD 1024x740, but that's all I know.
It's definitely something somewhere to do with the monitor or possibly powercord? Due to the fact that when the monitor isn't connected to the computer, it has "no signal", and even that goes dark.