Hello, I'm TV Tech1 and I'll be working with you to identify and help you resolve your problem.
It's probably not on it's way out...not at 5 years. But it does sound like it's within the range of needing a tuneup (like a car does) after it's been running for 5 years.
Since you can't get it off the wall, and it takes time to quit working, it's likely a thermal failure where the TV works for hours, then goes bad.
If you turn it off then back on quickly....and it works fine for a short bit...that's usually a microprocessor lock up.
If you have to turn it off and let it cool down for 20 minutes, then it runs fine for an hour, then it fails again....that's usually true thermal failure of a part on the TV set.
But there's a couple things you can try to ISOLATE the problem area.
Can you darken the TV room? Not pitch black, but maybe a stormy day kind of light level?
If so, do this.
When the TV works, and you just turn on the TV, look at the screen the moment you press the power button. BEFORE the picture appears, you should see that pitch black screen gently light up to a subtle gray light level. That's what we call priming the panel before the picture appears.
Priming is important. You don't get a picture until it's primed, and the sound usually follows immediately. So it's important to see what priming looks like, and when it fails....that's the time to --
1] Check and see if the volume bar or menu shows up on the TV screen.
2] Darken the room and see if the screen is gently lit/primed
3] See if you can hear the TV's sound or not.
Then, do you have manpower available to you in the future to remove the TV? You can't service it without a second man or 2 1/2 men (one to disconnect cables and power cords)