Gents,
I have good news and bad news to update. Let's start with the good news. Both Amr and Cyknight are correct. Touch screen could not display anything simply because it fails to locate the image file location in HC-250. When I unscrewed the TS housing box, I saw the power wire as well as the RJ45 connection port, which match Cyknight's description. Now the bad news, according to my new dealer pro guru, is that when the TS was hard reset, it actually went back to OS 1.xx compatible, which does not work with HC-250's OS 2.9.0. Even the pro guru couldn't get the image updater working after nearly 1.5 hours. In the end, he recommended that I should upgrade the home automation (with two option quotes, $9K or $11K). He also pointed out the switch was a managed one(?) that blocked his upload attempts (composer pro, image loader...etc). And the TS connecting to both PoE cable and wired power line is weird. Well, that ends this recovery operation, doesn't it? Even though I was thinking maybe another TS with working WiFi might do the trick. But it is really beyond my bandwidth and not worthy the time/money anyway. So I disconnected the power to the TS (both cable and hard wires), so it doesn't consume any more electricity.
I want to thank you all for your attentions and supports. It's time for us to move on. I probably will rely on the 4Sight subscription in my iPhone 8+ to manage the climate until we sell this house. In reality, I'll be more cautious when buying the next house that comes with pre-installed home automation.
Justin