Arduino Uno Pin 13 LED is always ON

My newly purchased Arduino Uno Rev 3 is suddenly not working. The built-in LED (pin 13) is constantly On. I can't upload any sketches and the hard reset button is not resetting the board. The upload stays busy with the error message: "stk500_recv(): programmer is not responding". I've checked other related posts on pin 13 op-amp issue and suggested work around, but none helped. Any clues on what my problem may be? Thanks!

When the opamp fails, that generally indicates that you have abused the chip - usually by exposing it to excessive voltages. On official boards, this will usually also take out the 16u2 resulting in the serial device no longer appearing. On clones with the CH340G, that will often survive - so it is more possible for the '328p and opamp to be trashed while the serial interface still works.

The board has been damaged. It should be replaced with a new one, and you should try to figure out what you may have connected incorrectly that damaged the board.

Thanks! The problem happened during the uploading of a sketch. As far as I remember, the board was only connected to the USB cable. I will try to get a replacement board.