Hi, I bought my iMac g5 (15") used a few months back. Everything worked fine. But recently it has been shutting off by itself and I can smell a light scent of something burning or something getting too hot! I can hear my fan(s) going but my istat is telling me its 143 F and I know that is way too hot! p.s. The imac will not shut itself off unless i leave it alone and it goes to sleep. It happens only when it sleeps or if i leave it alone for an hour.. Is there anyway that I can diagnose or troubleshoot this? I would hate to take it in. TIA!