My imac, after a year of reliable operation, has begun freezing at random intervals. Sometimes it works for an hour or two. Sometimes only a few minutes. Very frustrating. The light goes out in my mouse and the cursor no longer moves. Sometimes (but not always) it will start working again if I unplug the mouse and then plug it in again. I'm using OS 9.2.2 (because I like to use Hypercard) I've tried all the recommended solutions(rebuilt the desktop, zapped the pram and re-installed the system software). Any idea what can cause this? Could it be a virus?