lights working but still an error

Hi, for a class I recently downloaded the FastLED library and set up my Arduino Uno with a single LED from a strip of WS2812B lights. I have the light externally powered with 5 V. I upload an example sketch from the Example library which got my lights to turn on but when I tried to run it again this error...

An error occurred while uploading the sketch
avrdude: ser_open(): can't open device "\.\COM3": The system cannot find the file specified.

I went to check the port in tools and wouldn't let me click it anymore. My teacher recommended that I unplug the USB connecting the Arduino Uno board to my computer, close the sketch, open it again, and replug the device. It worked the same where it seems fine but then that error occurs. My teacher thinks it might have something wrong with the USB cord but it seems to be working fine.
The stuff below is the more detailed error (I clicked "copy error message") ...

Arduino: 1.8.13 (Windows Store 1.8.42.0) (Windows 10), Board: "Arduino Uno"

In file included from C:\Users\maggi\OneDrive\Documents\Students_Hue_Saturation_Working\Students_Hue_Saturation_Working.ino:2:0:

C:\Users\maggi\OneDrive\Documents\Arduino\libraries\FastLED/FastLED.h:14:21: note: #pragma message: FastLED version 3.003.003

pragma message "FastLED version 3.003.003"

^~~~~~~~~~~~~~~~~~~~~~~~~~~

Sketch uses 5818 bytes (18%) of program storage space. Maximum is 32256 bytes.

Global variables use 708 bytes (34%) of dynamic memory, leaving 1340 bytes for local variables. Maximum is 2048 bytes.

An error occurred while uploading the sketch

avrdude: ser_open(): can't open device "\.\COM3": The system cannot find the file specified.

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.

The error would seem to have nothing to do with that particular sketch. Can you upload an example such as Blink ?

For the board to show up in the IDE, it needs to be recognised by your operation system. So what does Windows Device Manager say about the board under the different conditions?

And I suggest that you provide a wiring diagram (photo of pencil and paper drawing is OK).