This has not happened to us yet. So ideas for troubleshooting.
I assume that you are getting no clicking or motor noise
when you hit the down button.
Two "easy" things come to mind. The fuse, and the switch.
If you can find the fuse in the electrical
panel, it might have popped. Ours are small blade circuit breakers, so easy to see if one has popped.
Then, I'd look to make sure the up/down switch is working properly. Pull off the cover and see if there are obvious contact to short out and engage the motor.
The TV is removable by lifting it up. This will give you more working room from the top. There is one screw holding the TV down into a v-notch. Not the four head
you see on the back, those are just for positioning. But, our single
screw was not engaged. So just gravity and a little bit of friction to overcome. Then, lift about 3 inches and pull out - toward cabinet front. Now you will have a lot of room to work
Also, it seems that the raising system might use a couple of switches - full up and full down - which tells the motors when to stop running ( only a guess ). Maybe something hit the fully down switch and the raising mechanism thinks it down. With all the wires running around back there, one could have hit it.
That would be the start of my approach.