My Intel Core Duo iMac (bought march 2006) is having some recurring problems with starting up and awaking from sleep. It's a 17" Rev A, 1.83GHZ, 160GB, with an extra 512mb of Ram added by me, running OSX 10.4.8. It has worked without problems for nearly a year but recently it just wouldn't start up. The power light would come on at the front of the machine, and just stay on with a blank/black screen for as long as I left it, until I force shut it down by holding the power button for 5 seconds. I can keep going through this process in the hope that it will eventually start ok on its own, but it never does. When I take the ram stick out that I added it will then start up ok. I can then put the ram back in and it will work ok for another few weeks before going weird again. In System Profiler it says that both Ram sticks are ok. So I'm not sure if it's bad Ram, and removing it makes the system work ok, or if just the act of removing Ram helps to get it going. I have done all firmware updates for Rev.A Intel Imacs. Though I only did the IFE firmware update recently after the problem started in the hope that it would help. Before I did the firmware update and was trying to sort it out it once got a grey screen and made a high pitched electronic sound, as well as not starting up and just getting a black screen I've also done a complete clean install of the OS, re-formatting the hard disk first. The machine worked fine for about a day after this but then I had to resort to removing the Ram again to get it to start up ok. Has anyone else experienced this or similar problems with their Intel Imacs? I'd be really grateful for any advice out there!