Hey Guys, I've got a 2008 aluminimum 24" imac. 3.06GHz, 4GB, 250GB. The screen started to just turn off around 2 weeks ago. Sometimes the machine would power on and work for around 1-2 hours, but sometimes only around 15 minutes. The screen just goes black. No funny flickering, no odd pixels etc. Just off. The superdrive is still reading etc, if I put in a disk it spins and reads, I can also hear the hard drive reading etc. I opened the imac and checked the graphics card. Its the 512MB Nvidia 880GS. I sent the graphics card to a company to test it and it worked directly in one of their machines for an entire day. I've replaced the ram and the lcd screen too. When I power up the machine I check the little diagnostic leds and it shows LED 1 - ON LED 2 - ON LED 3 - ON LED 4 - OFF but the screen is just black. Any ideas - I'm thinking it may be the logicboard but surely the dvd drive and hard drive wouldnt power on?