Hi everyone !! I recently decided to hook up my Arduino Uno to 12V that is coming from a car's power distribution module. I measured the voltage and made sure that the car is outputting 12V. So the Uno turned on a few times that I connected it to the 12V power jack. I could tell it was on because the green LED near where it says "ON", turned on. However, after a few times it turned off, never to turn on again via the 12V power from the jack. Curiously enough, when I Immediately afterwards hooked it to my computer using USB, It turned on. But it wouldn't turn on from via the 12V form the jack. Two interesting pieces of information:
I also noticed that the green LED light was slightly flickering when it was hooked to the jack, as opposed to when it is just on, when I hook it up via USB to my PC.
After Uno wouldn't turn on using the jack, my PC wouldn't recognize the board's COM port either and I couldn't select it in the Arduino IDE. I tried restarting my PC, but that didn't fix it so I ended up uninstalling the COM driver from the device manager and reinstalling it. This ended up working.
I would appreciate any hints or ideas about what is happening.