Arduino software won't find USB port

Hi, new to the forum and the Arduino platform.

I am using a Nano 3.0 and the latest version of the software on my Macbook. I am using the board to power a SureElectronics 8x32 matrix. I had everything up and running for a while, but recently it stopped working. At the time, the Nano was hooked into the breadboard and I was playing around with an LED, plugging and unplugging it to the power source of the Nano. All of a sudden, my nano and matrix board stopped working. The board flashes an orange led and the green power led is on. I uninstalled everything, reinstalled the software, including the FTDI drivers, and yet, the software is unable to find the board for me to re-export the code to the chip. Any ideas?

Nobody can help?

Use a multimeter and check things like the 5V and 3V pins when connected to USB.

Too late now, but this should be a lesson in never changing connection while being powered.