Why have my rear usb ports stopped working?

This is a computer for business use only so there is no abuse to the machine as far as downloads or other recreational fun. It was working fine all day long and and after about an hour of not using it all of the lock symbols on the key board lit up (caps lock, scroll lock, num lock). None of the keys were responding but the mouse still worked. I rebooted the pc and it would not start up. It kept getting to the configuration step and saying keyboard failure. I unplugged the keyboard and swapped it with the mouse and the computer started fine, but now the mouse wont work. I have four usb ports in the back of the pc and all of the sudden three of them went out. I did not change any settings or mess with anything. What can cause this and how can I fix it?