Well, I am going to say just a guess, since you installed everything new again, we can rule out virus attack. Next, it sounds to me like a voltage problem, the ports work when at idle, but as soon as you plug a drain source on them, they quit. I would try to see if there is voltage settings in bios, if you have the usb expansion card, try unplugging it, and use the front usb or in the back by the mouse and keyboard ports. I don't know much about the voltage end because I do not know your board, but hey, its worth a look. Be sure to have updated drivers for your usb, if your using XP, then it will do it automatically. Hope I helped out some.:)