Windows frequently rebuilds it's icon cache for various reasons that are a bit of a mystery
I think that in this case you are unusual for having so many flash files in one place. If you want to stop it from doing that you can select the "Always show icons not thumbnails" and Windows will stop trying to open the files and render them to get a thumbnail...
Your idle temp of 50C is a bit high to start with. 15C in crease for rendering 150 flash files to get an icon I would expect to be normal. But you should be idling around 30 something I would think. As others have suggested, make sure your fan is clean and that there is airflow through your case. Including around your case (If your case is under the desk it may be re-breathing it's own exhaust and that'll keep the temps high.