There is no USB serial port thing showing up in Tools-->Port. Arduino Uno

I am very new to Arduino and programming in general so I have absolutely no idea how to solve this problem. I followed the Getting Started guide step by step until I realized something was wrong. It appears that there are no USB ports being read by Tools-->Port in the Arduino application. It shows in Port:
Serial Ports (Serial Ports is faded for some odd reason)

I have also tried FTDI drivers, with no success, and been searching on how to solve my problem. Nothing seems to be working, so I have decided to ask myself.
The Arduino Uno has been plugged into the computer while I've been trying to solve the problem, unplugging and plugging it back in, restarting the computer, re-downloading the new Arduino software. Interestingly, about 3 weeks ago when i didn't have the Arduino Uno the ports showed up just fine. It doesn't work now, no matter if its plugged in or not. I am on an iMac, OS X Yosemite version 10.10.3