[Elecraft] RS-232 communication failure

[Per Enocson]

Back from my summer vacation, my K2/100 and PC don´t get along anymore.
Everything else works fine, also the communication between the K2 and the
KAT-100, although initially there was a slight trouble with the keyer (no
dits or dahs,just one steady note, whichever paddle pressed). I have tried
with three different PC:s and with two different cables (one built new for
testing). I am convinced that the PC communication settings are correct. I
have followed the troubleshooting suggestions.  Any suggestion on what to do
next is very much appreciated. E.g. how do I conclude if this is a hardware
or a software issue?  Are there any known compatibility issues between
firmware 2.04 which I recently installed when doing the keying modification
and the  1.06 firmware (old) of my KPA-100? Thanks  Per SM0WRA K2/100 no
1623