timeline: im working on a friends iMac g4 flatscreen. she told me it wouldn't start up at all, but when i pluged it in it worked fine. i thought she was crazy, but after using the machine for 5 hours it lost all power without warning. it refused to start up for 10 minutes of unpluging, disconecting mouse&keyboard, pluging it all back in and pressing the power button. i want to say it's a hard drive failure, but i'm not certain. are there any tests i can run or system logs i can check to verify that this is a hd failure? what else could it be?