So I'm a very early beginner (I started messing around with my new uno only about an hour ago) and I was going through the steps in the Mac Osx beginner guide. I got to the last step (testing the sample code) and neither the tx or rx LEDs lit up. I realize now that the guide is probably a bit out of date, the code was working fine but lighting up L instead of TX or RX. So, me being the beginner (idiot) that I am I try to figure out what I did wrong. I thought that maybe I chose the wrong port (even though I disconnected and reconnected the UNO to be sure when I first set it up). I thought I might as well try a different port and selected the other dev usbmodem port. The instant I uploaded the program my screen went black and I'm only getting a blank white screen on restart. Please help.
Have you unplugged it?
Try restarting the Mac in safe mode (hold down Shift after you hear the startup tone).