回答“CPU upgrade 2.0GHz to 2.8Ghz ( C2D Extreme X7900 )”Hello, I’m sorry for resuming an old thread, but i recently tried to do this upgrade; I have an iMac mid 2007 20” with an intel T7300 cpu, but after the upgrade to an X7900 cpu the iMac do not want boot. I opened and re-closed the Mac many times for checking if i reconnected in a wrong way some connector, but nothing changed; Then i tried to power up the iMac without the front case for checking the 4 internal led and i noticed that the 4th stay off, so I checked the lcd connector many times, but no way to solve the problem. When i press the power botton this happend: I heard the ODD’s sound, The cpu fan try to spin but it don’t do it, no chime sound, the first 3 led turn on and the 4th not, black screen and nothing more. After two days, i decided to replace the new cpu with the old one and the system suddenly restart to work. What’s going on? It’s the new cpu that doesn’t work or my iMac do not support it? Apologise me for my bad english.