Arduino Uno R3 not recognized by IDE and led flashing

I have an Arduino Uno R3 that has been working fine for a couple months. I just loaded a sample ir receiver/transmitter example sketch and disconnect the board from the computer and powered it using a battery. The sketch worked but after I reconnected it to the computer the board will not appear under the Serial Port tab in the Arduino IDE and the led for pin 13 flashes rapidly but very dim. If I reconnect it or hit reset the led flashes (full brightness) like it normally does when starting up then after a second goes back to flashing dim and rapidly.

Thank you,
Jacob Schuler