IMac 24'', late 2008. 3,06, 4GB RAM, 500 GB hdd (100 free). After working on my iMac for half an hour, or so, the system starts to slow down and freezes. It won't even boot (just getting the white screen with the Apple). Won't even boot from CD-ROM. If I wait for a few days, it comes back to normal, but after 30 min of work same problem. Tried all the funny boot options with the keys. The Apple Store couldn't find any problems on it, but they only had it for 15 min, and on 'a good day' Could it be damaged RAM, or ..?