It might be a good idea to first: visually inspect all of the USB ports for damaged pins or shorting pins. It is easily possible to plug in usb flash drives or cords inocrrectly and damage/bend pins so they short. A single bad usb port could be affecting all of them, I see this all the time. They might not RMA the board if it has a physically damaged USB port, I have never sent a board in due to this so I can not say for certain.
If no pins are bent or shorting in any of the usb ports, test a keyboard to try and get in the bios as others have mentioned. If no usb port works with a keyboard at a bios level, your board has a problem and you should be able to rma it if it is still under warranty.
Also do not forget to inspect inside of the computer look on the motherboard where the front usb ports plug in (usb header on the board). Inspect the open usb headers as well. I have seen some bent usb header pins on a board, the usb ports were not working. The pins were touching (shorting), I bent them straight so they were no longer shorting and it all worked again.
Edited by zingo156, 10 April 2014 - 02:03 PM.