When Arduinos are plugged in on Windows machines, their USB port will be identified as COMx, where x is a number between 1-??? (I don't know the upper limit, but would suspect 256 or smaller).

Every Arduino you plug into a given machine will have a different COM port number. Note, plugging the same Arduino in on different windows machines will most likely cause that Arduino to be mapped to a different COM port number. If it happens to get mapped to the same number on multiple machines, it is by coincidence only.

To identify which COM port number, open Control Panel, System, Hardware, click the + sign to expand the COM ports. Do this before and after you plug in the Arduino. You should be easily able to find which COM port is assigned to the Arduino.

If you still have problems, send me a PM to remind me. Sometimes I forget which messages I reply to, so I don't always look for replies.

perfect! just finished it, thanks