Okay, there is a problem but not with the DCS. It should run in conventional mode, no matter what, if the teather is okay, track is properly wired and no wires/connections are damaged, among other possible issues. I am guessing the engine has a 5v control system. It could be an issue with that since it doesn't run at all.
Make sure your power supply is good. Try running a different engine to make sure. Be sure you have clean wheels and clean rail. I understand you may have done all this, I am just trying to eliminate issues one at a time.
I am surprised none of the more technical guys have not jumped in here. Perhaps in time...
Tom