Code not uploading to Arduino UNO

Hello,

Up until 11/6, my Arduino UNO was functioning properly. On 11/7, I attached an IO Shield, and my MATLAB/Arduino IDE code would no longer upload to the Arduino. I would get the following error:

Arduino: 1.8.9 (Windows Store 1.8.21.0) (Windows 10), Board: "Arduino/Genuino Uno"

Sketch uses 3894 bytes (12%) of program storage space. Maximum is 32256 bytes.
Global variables use 220 bytes (10%) of dynamic memory, leaving 1828 bytes for local variables. Maximum is 2048 bytes.
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x99
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 2 of 10: not in sync: resp=0x99
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 3 of 10: not in sync: resp=0x99
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 4 of 10: not in sync: resp=0x99
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 5 of 10: not in sync: resp=0x99
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 6 of 10: not in sync: resp=0x99
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 7 of 10: not in sync: resp=0x99
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 8 of 10: not in sync: resp=0x99
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 9 of 10: not in sync: resp=0x99
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x99
Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.

However, power is going through the Arduino (green light is on) and MATLAB recognizes that the Arduino is connected via USB ("Arduino Uno is connected"). If I type a=arduino() into the command window, I receive an error.

I went through the troubleshooting page and several discussion boards, but nothing I did helped connect the IO Shield/board to the computer. I then disconnected everything from the Arduino, including the shield, and attempted to upload code. I received the same error. I then attempted to re-install the Arduino hardware package, but I could not download it due to the same error as above.

Notes:

Tools >> Board: Arduino Uno/Gemini
Tools >> Processor: AVRISP mkll
Tools >> Port: COM4

The Com Port is showing up in the device manager.

Any ideas?

re-boot PC ?

ieee488:
re-boot PC ?

I've tried this many, many times

Try on another PC ?

Start by removing everything connected to the arduino then try this:
Take these steps: Power off the board completely (remove the USB cable). Hold down the Reset button,
keep it held down (or, run a jumper wire from the RESET pin to the GND pin). Still holding down Reset,
reconnect the USB cable. Start uploading a sketch that does not have this problem (I use the Blink sketch).
I have seen this happen several times when I flood the serial output. An indication is the tx light is on. My quick fix is to add a 5 second delay in the setup then I can reset and gain control before the serial port floods. Secret do not keep the console constantly busy printing.
Good Luck & Have Fun!
Gil

gilshultz:
Start by removing everything connected to the arduino then try this:
Take these steps: Power off the board completely (remove the USB cable). Hold down the Reset button,
keep it held down (or, run a jumper wire from the RESET pin to the GND pin). Still holding down Reset,
reconnect the USB cable. Start uploading a sketch that does not have this problem (I use the Blink sketch).
I have seen this happen several times when I flood the serial output. An indication is the tx light is on. My quick fix is to add a 5 second delay in the setup then I can reset and gain control before the serial port floods. Secret do not keep the console constantly busy printing.
Good Luck & Have Fun!
Gil

Hey Gil,

Thanks for the advice. Unfortunately, it still isn't uploading :(. Any other tips?

ieee488:
Try on another PC ?

I could try this, but I only have the 1 at the moment