bulletsmith
Master
Do you have another coax cable on hand?
If so disconnect the current coax that is going to TV3 at the splitter (but leave in the wall/in place).
Connect the new coax cable to splitter (same port you disconnected) and then connect to TV.
You will probably have to move TV into that room to test.
Does the TV work again?
If so then your current cable in the wall or the terminations are bad.
If no then either TV or spliter have gone bad. Suspect at this junction its the splitter.
Try a different port on the spliter to see if that helps.
Could also be as simple as a single strand of shield touching the center conductor on your newly installed connector....