Chosen Solution
My Early 2009 iMac (3.06 GHz Intel Core 2 Duo) has recently had an extremely loud fan. Using a fan utility I can see that its the CPU fan that is running at max. After a period of time, the screen will go to vertical lines and fan is off. I’m wondering what makes the fan run high in the first place- and why does it shutoff eventually? How can I diagnose? I’m unable to boot into diagnostic mode, that appears to be something added in later models.
My best guess wold be that the CPU is hitting its T-Junction and shutting off. Before it shuts off, can you see what temperature it registers at before it shuts down? It is also likely the Graphics Card is hitting its thermal limit, hence the vertical lines. Try using a program like AIDA64 to monitor theses temps. If its anything above 80C after startup, you have an issue. Good luck!
