I have a relatively new problem on my hands. I cannot write software to my arduino uno, despite having power from USB and not having anything in RX pin 0.
The arduino pops up in my device manager under COM3 everytime I plug it in, however, when I first plug it in, or try to upload software, the TX/RX pins never blink, and I always get an avrdude "out of sync" error.
The only thing different as of recent was running the Arduino Uno from a 12V project lithium ion battery.
The arduino was warm to the touch after using this type of battery for about 5 minutes... starting to get scared that something fried perhaps.
The board type and correct com port show in the tools setting.