Best guess is the USB Com ports been highjacked by another process..
Have you installed anything recently??
If you know how to use a terminal window you can see whats connected by listing by using ..List the USB
$ ls /dev/tty.usb*
/dev/tty.usbmodem14121
If the boards connected you get this..
If not connected you should get an error no device .
My guess is you will get a device connection then your half way to finding out whose pinched it..
happy coding 8) 8)