mac pro usb ports not working

Hi I have a dual core intel mac with 3.0 ghz processors 8 gig of ram v1.1 all of the USB ports front & back have failled. The computer boots up into Snow Leopard, 10.6.8 The mouse, keyboard or any other devices using USB ports don't work, I checked with a multimeter on all the USB ports & there is no +5volts between pins 1 & 4 on any of the USB ports. I have check the keyboat & mouse on another mac & they work fine.

Doy you have any idea what I should do now,

Kindest Regards,

Anthony.