COM5 vs other COM

Hi there,
New to Arduino, enjoying it. Going through the tutorial I got stuck at the projects running a 9 V motor (MOSFET and H-bridge). I was getting garbage reads when I set up a monitor watch or no communication at all.
I decided to look at the USB connection and changed the COM port to COM4 from COM5 (Arduino). Big mistake! Now I can't get COM5 to show up. I tried device manager (running a Window 10 Surface Pro), manually change the preference txt document under the arduino tools, do a clean install. Aerduino insist on COM4 and doesn't give me the COM5 option.
Any help would be appreciated.

Welcome to the forum

Do you care which COM port you use as long as it works ? Does Windows create a new virtual COM port when you plug in the Arduino and does it show in Windows device manager and in the IDE ?

Hi! Welcome to the Forum!

This is a common symptom of baud rate mismatching between what is set in your code and what is set in the Serial Monitor. If you have this line in your code:

Serial.begin(speed) 

This speed must be the same that is here:

THX. I don't care but using COM4 or 3 doesn't even power up the board. COM5 when working was powering it up and in the Tools -> Port: it showed "COM5(Arduino). It was working fine for all the tutorial projects up until the ones using the externally powered motor. I am trying on another computer but COM4 is already selected and trying to load an example sketch times out, with no lights on the board. I should say I use 1.8.19

THX,
The baud rate is correct. I always start with
Serial.begin(9600);

That makes no sense. The USB lead supplies power independently from the data connections. Indeed, it is possible to power an Arduino board with a USB lead with no data leads in it including from a power bank that has no data connections

Unless if, for some reason, the board is fried... :face_with_diagonal_mouth:

So here is what I did: because I was stuck at the "zoetrope" project that uses an H-Bridge to drive an externally powered 9V motor, I had the board all wired up according to instructions. I was trying to solve the COM issue using the wired up board. Now I completed remove all connections and have a bare board. This time both computers can see the board (green light) and COM5 came back.
Easiest explanation is that I did something wrong while wiring the board.

That was my HUGE worry!! but see my reply to UKHeliBob: using an empty board solves the issue. Thanks both for your help!

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