First you have to convert you wincmd.key into a wincmd.reg Windows registry file - you can do that with this tool: https://madsenworld.dk/tcmd/tools/wincmd_reg.zip (don't ask me where I got it from - but it works).a question, how do you get your key in the registry?
Put wincmd_key_to_reg.exe and wincmd.key in the same directory and execute wincmd_key_to_reg.exe and wincmd.reg is created - now double-click on wincmd.reg and answer yes to the questions. Rename your wincmd.key file in your TC directory and restart TC and see if it worked.