Diagnosis
This is a classic 'soft-brick' or boot loop issue. The TV's internal processor or software is stuck trying to start up, so it's partially on but the screen and controls are dead.
How to Fix It
You need to force a full power cycle to clear the memory. First, unplug the TV's power cord from the wall outlet. Don't just turn it off at the remote. Wait a full 60 seconds—go make a cup of tea. While it's unplugged, press and hold the physical power button on the TV itself (on the back, usually bottom center) for 30 seconds. This drains any residual power. Now, plug the cord back in and try turning it on with the remote. It should boot up normally.
If That Didn't Work
If the red light is still just stuck on, the problem might be with the One Connect box (if you have that model) or a main board issue. Try unplugging everything from the TV—all HDMI cables, the ethernet cable, and the antenna—then repeat the full power cycle. Sometimes a faulty signal from an external device can hang the system during boot.
Heads Up
If this happens repeatedly, there's likely a firmware bug. Go into Settings > Support > Software Update and turn on Auto Update once you get it running again to prevent it in the future.