After over five years of flawless performance and reliability, my 30" ACD has started to black out-- first, after several hours: it would fade to sleep and can only be turned on again by having the power cable unplugged, and plugged in again (to the power socket). And just now, it will black out within several minutes after the unplugging/plugging. Has anyone had a similar problem? Could it be that the power adapter/ bar that needs to be replaced? Or is it the internal power supply? I've checked the Apple boards, and some have/ had similar problems, but the majority are with the newer 27" Thunderbolt Displays, not the older 30" ACD. Any info would be very much appreciated!