Sometimes on startup, Ubuntu does not recognize my USB Keyboard & Mouse. This problem is frustrating as Windows seems to recognize them.
It took me a while to recognize the root of the problem was with the USB 3.0 ports on the Motherboard. By moving the usb connections to the USB 2.0 ports on the motherboard this problem was solved.
Problem: USB Keyboard and Mouse dont work on boot up.
Solution: Move the connectors to the devices from a standard USB 3.0 port to standard USB 2.0 port(check with your motherboard manual for specifics)