My Imac 24" (2008) LCD turns black and sometimes it turns on again (there's no regular pattern in this failure). I have an external Apple Cinema Display connected to the iMac and I can control it perfectly. The iMac works very well except the display. I went to Apple authorized repair centre and told me the problem is the display and they changed the LCD but the problem persists. I've done all the procedures suggested by Apple and online posts about similar problem (PRAM, CMOS, checked fan rpm, system permissions…) with no success. I went again to the Apple authorized repair centre reporting the problem and the guys checked again everything (even the power supply) and said it's everything ok with the machine and can't find the problem!!! They also told me that they have direct communication channel to Apple assistance and they have no reply (really strange!!!). I noticed identical cases reported on the web but also can't find a solution. If someone have a suggestion I'll appreciate!!!!