my intel core 2 duo 2ghz imac went from being fine to dramatically slowing down and pinwheeling like crazy. shortly after that, it just wouldn't boot up (just a gray screen with the circle of dashes that go round and round). so, i reinstalled the OS from cd-rom. then it was fine for like a week or so. then the cycle started over...pinwheeling, then won't start up, then i reinstall the OS. i've experienced this cycle like 5-6 times now. but today, it didn't start up and i got the folder icon and question mark. so i reinstalled the OS and for now it's fine again. any idea as to what the issue is? oh, i also got techtool pro and ran all of the diagnostic tests...they all say everything is fine and dandy. help!?!?