hey all. i need some serious help. my iMac G5 (20" no isight) is having some issues. it will randomly without warning or reason shut off. like a power failure. i checked all cords removed the circle white thing on the power plug to make sure it is pushed in. re0installed mac osx and its still shutting down. it happens mostly when you leave the computer alone for a little wile. any help would be amazing! thanks