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Had this exact problem when I changed to a new laptop. Had an rs232 adapter that worked fine on my old dell, got a new laptop with a newer version of windows, got the no com port available message, couldn't read or write the powerfc file. Had to get a different serial-usb adapter.
I am willing to bet that it is your usb to serial adapter and its drivers.
I have had great luck with this one from belkin and i have used it on other equipment and it is the only one which consistently works with every computer i have used.
and it comes with the cd with the drivers on in case your computer wont install them automatically.
Belkin USB-to-Serial Portable Adapter for Notebook with LED Indicators
my laptop is windows 10, and it likes to forget to use the driver for the cable which works, and use the stupid default one which doesn't work.
so once in a while i need to go into the stupid menu and delete the stupid driver and then restart everything and it finds the correct driver and its fine.
not sure why it does it, or why this is even a thing, this is like stuff that we were dealing with in the 80's to play like space quest...