USB Ports not working

i have a computer that i am working on that non of the usb ports will work. i have looked in the device manager and they show not errors i have also uninstalled and reinstalled them, i have also gon as far a refomating the computer, and they still dont work. any thoguts on how to get them to work. on any usb optical mouce or any usb key that lights up when you have it plug in is blink once as soon as you plug it in help.