I have an iMac G5 that is starting up, then working okay for 1-2 minutes. After that, the processor usage goes way up, and the fans start spinning loudly. It's a first generation 1.8 GHz with a 17" display. Mac OS X Leopard. Recently, it spun up and then shut down and wouldn't start again. The room it's in is < 75 degrees F. No malodor, or other symptoms save for hot to the touch. Has been left shut off and unplugged for a few hours, and still has this problem. Any help would be greatly appreciated. Thanks!