Mac trouble finding USB device

Running a MacBookPro 10.9.5 OS and a UNO board. Tried every combination of serial port and boards from the tools menu with the same result: avrdude: usbdev_open(): did not find any USB device “usb”. Just bought the board today and never able to get it to operate. Help! The power light comes on when plugged into the USB port, and the “L” LED flashes continuously.

Also running a MacBookPro 10.9.5 OS and a UNO board. Also tried every combination of serial port and boards from the tools menu with the similar result: an ERROR MESSAGE saying Serial Port already in use.

When I pulled down the TOOLS Menu, under Serial Port I had no choices that have worked. I also just bought the board today and cannot UPLOAD a properly-compiled program (Blinking LED) to the UNO board.

I've pressed the RESET button and connected and disconnected the device and opened and closed the IDE.

Same here. I'm new to using Arduino boards and just got the Uno last week. I'm trying to run the test program "Blink" and I can't find the correct serial port using a macbook pro with 10.9.5 OS. I'm thinking of upgrading to the new OS Yosemite if I can't find a fix elsewhere in the forum.