Please try this experiment and then report back with the results:
This procedure is not intended to solve the problem. The purpose is to gather more information.
- Connect the Arduino board to your computer with a USB cable.
- Press and release the button on the Arduino board that is marked "RESET".
Now please reply here on the forum thread with the answers to the following questions:
- Did you see the LED marked "L" on the board blink immediately after you released the "RESET" button?
- Did the LED blink only once, or did it blink multiple times quickly immediately after releasing the button?