I've just received my Uno today and already I think I may have broken it :(

I was able to connect to usb and upload a sketch (the blink). However, I then tried to connect a circuit to do the Hello World LCD example. After trying this a few times, I noticed the LCD chip get very hot...and I had mis-wired it. In any case, after a few more tries, the USB connection to my Arduino UNO stopped working.

I tried swapping the cable, connecting it to another mac and to a windows with no luck. I'm worried I may have shorted the USB bus chip when trying Hello World.

I also tried connecting a 12V DC power supply.

I still get the green power light and the amber L light... Did I break my Uno? How do I troubleshoot this one? thanks