If your TNC is permanently in Kiss mode then Putty probably won’t work. Putty over the serial port is looking for a standard serial to device connection, not kiss. The only thing that will talk to the TNC will be a program that speaks the kiss protocol.

If you are using a USB to serial adapter, keep in mind that if you remove the USB plug and plug it in to any other USB port it will then get a new com port assignment in most cases. If you are using a USB to serial adapter also check to make sure that adapter is not one of the prolific chipset models.  There was a problem with counterfeit prolific chipsets so Windows updated the drivers to validate the chipset and if it was a counterfeit the driver won’t work (there is a way to use old drivers but you have to look up how to do that). For newer versions of windows it is best to get a newer SUB to serial adapter that uses the FTDI chipset.

Brian N2KGC