I recently upgraded from 13.10 to 14.04 and now I have to unplug the keyboard and mouse and plug them in after the system is booted. I have a Razer Black Widow keyboard and a Corsair mouse. My system is a dual boot Ubuntu/Windows 7 - i7-4770 in a Dell XPS8700 I have no problem with Windows and the USB problem(I assume it's a USB problem) only started after this upgrade. I'm not very familiar with Linux software repairs although I've used Ubuntu for years. I'd like to continue to use it without wearing out my USB ports
I was having the same problem with my XPS8700 in a dual boot with Windows 8.1. What fixed it so far was disabling acpi when booting Ubuntu.
It worked for me, hope it helps!!!