Hi everyone. I've been using Apple products since the Apple IIGS while in school. I have plenty of experience installing stuff like ram, hard drives, processors, etc. In other words I don't repair macs for a living but I know enough to do upgrades and installations on most computers. I'm currently typing this post on an old Beige G3 that's has been my frankenstein. This honestly shouldn't be an issue, but it is. I'm hoping to tap into the wisdom of some of the more experienced users here in this forum. If you'll indulge me, I'll start with my story: I own a late 2009 iMac with a 21.5 inch screen. (See link for full specs - http://www.everymac.com/systems/apple/imac/specs/imac-core-2-duo-3.06-21-inch-aluminum-late-2009-specs.html) For the first time in my life, the SMART sensor on a hard drive has actually warned me about a hard drive going bad before dying. The original internal hard drive was a 500GB Seagate SATA that was installed by Apple. While I had the time, I ordered a 3TB Hitachi Deskstar NAS SATA as a replacement. To avoid any issues with the iMac's fans, I ordered from OWC a special kit that includes a special digital thermal sensor that prevents the fans from running like crazy. Installation went as well as could be expected. I took my time and followed the installation video that OWC had and referenced an install article posted on ifixit.com. The only trouble I had was plugging back in the ribbon cable that connects the LCD screen to the motherboard. On the first try, I crinkled the end and had to smooth it out with my fingers. (That might had been a fatal mistake.) I was finally able to plug the ribbon cable back in with a pair of tweezers. My iMac powered on and booted from an external drive like it was set up to do. I was able to successfully reformat the new internal hard drive without any issues. I ran Carbon Copy Cloner to clone everything from the original hard drive to the new one in the iMac. When I got back from the shower, my iMac was stone dead. I tried a few things like forcing a reboot, trying another outlet, and letting it rest for an hour and two then plugging it back in. Nothing. Not even a sound. I haven't cracked it back open because I see no benefit to doing so as of yet. Unless I find something massively obvious. I've done some online research and found a this thread >> http://forums.macrumors.com/showthread.php?t=941281 that had another person with a similar issue. In the end, he had it repaired by the Apple Store and they claimed that the LCD power inverter cable in far enough and that blew out the power source. I'm not sure how plausible that is, but I've never had any major issue after installing a hard drive, ram, etc before. Even though it would make sense to install a new power supply, I honestly don't want to waste my money on a new power supply if that's not really the source of my problem. Or worse yet it doesn't correct the problem and gets blown out. I am seeking estimates from different repair shops in my area. I honestly rather fix it myself. Any suggestions or ideas would be greatly appreciated. Thanks in advance!