If there are no serial devices listed that have only the first letter capitalized, then the last Teensy program did not enable the USB serial device. There may be other comN ports listed (all lower case), which are not Teensy USB serial devices. Any COMN devices (all caps) listed are FTDI serial ports. If there is a ComN device listed skip to the end of the page.
Select the Control Tab, and select the Teensy device you are using.
These 2 popups below will appear. To initially load a program that enables the USB serial device push the button on the Teensy.
After the button is pushed the Options menu will now reflect Teensy options and will show a ComN port (first letter capitalized) as a Teensy USB serial port.
If you do not see this ComN device, then communication has not been established.