I had a lot of fiddlesticks getting JMRI setup, my first PR3 broke, got a new one, setting it up I used an offbeat extension cable I think I fried something, dunno, sent in digirax replaced it, I bought 2 backups. If one dies I wont be months out of one jabbering with Digitrax trying to replace.
JMRI is awesome, I have it, it took some learning curves but once figgerred out it will do good.
I have target signals working for a yard ladder module, getting ready to install detectors, lighting, get this module the workout.
The com port setup for me if it failed I deleted it, it advanced the port number, I ended up at 14 now. The port is virtual using the USB. If you boot the computer and JMRI complains it cant find the port, pop USB connector out for a second, then replace it, then reopen JMRI. Be sure your DCC system is powered first before computer booting.(I use digitrax super chief)