Possibly the thing that connects the monitor with the computer (does the whole computer work other than the monitor?) Is damaged and is probably providing or consuming low power from the supply

If your really sure it's working, Its pretty simple. You have to replace your TV screen.

You put it on for to long? Your motherboard and display or the chain that connects them both is cut off in some way, since it didn't fall according to you keeping it on for too long makes OLED screens heat up and slowly burn away. You need to replace the one thing you bought the Steam Deck for which is the OLED. Should start working. Keep it up and it'll spread like a virus. Kinda already spread since you said the fan was acting weirdly. Better find a replacement for the screen now

The problem is either with the thing that pumps soap or the sensor. You probably need to replace your sensor. You should troubleshoot it before you replace the sensor.

There is technically no answer to this as Samsung has a very strong PIN protection. You need to get it factory reset (deletes all your data) so you can crack the lock and get in.

Use your remote and press the Power button on it and aim the remote at the red light. Should work