Ursprünglicher Beitrag von: Dan ,
From your description it sounds like the graphics card needs replacing. That would be the cheapest solution here. Finding the correct one may take some effort. Click on the first link I posted as your system came in two different configurations if you can get to the about this Mac menu and then clicking on the hardware details you should be able to figure out which you have. Otherwise, you'll likely want to look at replacing the complete logic board if you can find a cheaper one clicking on the second link for the other systems with in the series. Here is the steps to open your system: [guide|1852|iMac Intel 21.5" EMC 2308 Logic Board Replacement] and then from Step 34 follow this guide: [guide|6272|iMac Intel 21.5" EMC 2389 GPU Card Replacement] picking it up at Step 44. You will need to clean & apply a fresh coat of thermal paste follow this guide on how: [guide|744|Technique: Applying Thermal Paste]. I do recommend you use the [product|IF179-010|Arctic Silver Thermal Paste] and the [product|IF179-023|Arctic Silver ArctiClean] cleaner. And lastly, if this is too big a job or too expensive then I would recommend looking at a used system.