Suddenly unable to upload to Uno via USB COM port

Development Tools IDE 1.x
1

I've been working on an Arduino Uno project, and I've uploaded many code versions over the past week. Then today, after ~1hr of more iterations, I tried plugging the board back into the same USB port and uploading the new code, and I got:

Archiving built core (caching) in: C:\Users\benla\AppData\Local\Temp\arduino_cache_468985\core\core_arduino_avr_uno_a94ab6aaf61dfb93b4a8079c694a14c2.a
Sketch uses 23932 bytes (74%) of program storage space. Maximum is 32256 bytes.
Global variables use 1126 bytes (54%) of dynamic memory, leaving 922 bytes for local variables. Maximum is 2048 bytes.
avrdude: ser_open(): can't open device "\.\COM4": The system cannot find the file specified.
Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.

The Tools/port menu is grayed out. I've tried restarting everything, plugging and unplugging...Windows is passing power, but it doesn't recognize the device (Uno). The USB port on my computer works if I plug in an external drive. When connected to the computer, the Uno lights turn on, and the latest build that I upload is running properly - sending SMS messages. I can hit the reset button and it flashes near Digital Pin 13 and looks like it's working. I've tried disconnecting the shield and all connections and uploading to a bare Uno board, but I get the same error. I tried everything on the Troubleshooting guide - except updating the driver...I couldn't figure out where the driver is stored in Windows, and the Uno doesn't show up in my device manager under the USB/COM port.

It was (is) running a FONA800, temperature breakout, LCD breakout, RTC breakout, water sensor, and Featherwing relay that switches the FONA circuitry between "Charge" and "Run." Any ideas? Did I overload the Uno?

2

Are you using any of the Analog pins for whatever your running?

3

I was using A0 (monitoring a water level sensor) and A1 (monitoring Vin so I know when it's plugged in and when it's running on battery). But when I started troubleshooting, I disconnected everything, so it's just a bare Uno board, nothing plugged in.

4

What does DEVICE MANAGER show when you plug in a bare board ?
Have you tried other cables and USB ports ?
What was the last sketch you sent up to the board ? Use code tags to post it back here ( </> )

5

Actually, I just went and bought a new Uno board and it works great. So I'm not sure what I broke on the original Uno but it was definitely the board.
Thanks for the help anyway

6

It sounds like you blew the usb-serial adapter chip - if it's a genuine board, that would be an atmega16u2 (running firmware that makes it act as a usb serial adapter), for clones it is usually a ch340g or cp2102. For what it's worth, based on the number of people here who manage to break the usb-serial adapter, it seems to be more fragile on the 16u2-based boards than on the cheap clones. Usually seems to happen when the power rails are abused (electrically, eg, overvoltages, spikes, etc), particularly while it's connected to USB.