I think it is a well-known fact that the 2006 Intel Core 2 Duo iMacs have defective GPUs, where a high percentage of those in use fail. Apple has done nothing to address the issue, and they won't replace defective models for free, especially now, when they are 8 years old. Symptoms of the defective GPUs include, but are not limited to lines across the screen, graphical glitches such as distorted graphics, freezing, randomly rebooting, kernel panics or randomly shutting off. Aside from the 24" iMacs, the GPUs are soldered on and cannot be easily replaced. It is best to replace the entire logic board, which will cost more than the computer is worth. 24" iMacs of this model have slotted GPUs, which are more easily replaced, but they still require the same specific model of GPU, and finding a good, working one will be hard. I know that this issue is heat aggravated; installing smcFanControl may help to temporarily solve the issues that come with the defective GPUs, but it isn't a permanent solution, and won't always help. I may try reflowing the GPU solder in the future to see if this will fix it, but for the time being, you can disable the GPU in order to get the computer to at least function. For those who still use the 2006 iMac and wish to continue using it or cannot upgrade, you can try the following: Click the Finder icon in the dock. Open the System folder, then the Library folder. Search for a folder called Extensions and open that too. For those with the ATI X1600 GPU, look for a file called "ATIRadeonX1000.kext". Remove it from the folder. I kept the file in my Documents folder, just in case. Now, reboot the computer for it to take effect. For iMacs with the nVidia GPUs, find your corresponding kext file with the corresponding GPU series. If you reinstall Mac OS X or upgrade to a newer version, you will have to do this again. Note: This essentially disables the GPU and moves the load to your CPU, so you should not experience any major graphical glitches, crashes or shutdowns, among other issues associated with the defective GPU, which will make your computer usable again. Just know that you will not be able to watch YouTube videos (oddly though, you can still watch the YouTube advertisements without any problems), you won't be able to watch DVD movies and you can't use iMovie, and some UI animations will not be fast. You can still run many other applications, and even FaceTime still works. For the most part, other applications, such as Safari, GarageBand and even Logic Pro X do work well with disabled GPUs. I don't know how permanent this solution is. I've had my iMac's GPU disabled for about a month now and I've had no problems with it, and I don't have to keep my fans ramped up all the way. This is just a little thread that you might find useful.