Why does it turn on at random with volume going to 100?

First remove the batteries from the remote and see if that fixes it, if not its either the sensor board or main board

Fault to its main board. Short circuited component/s at it. Contact any service technician; or the authorized service center. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. http://electronicshelponline.blogspot.com/ . In most cases, the main board might have to be replaced. If so, a software [firmware] update too might be necessary.

Claim lightning damage, put old boards back in it, sell new boards on ebay while a shop fixes the set for free (minus deductible paid for by selling ebay boards). Tada, repaired!

Or just sell the panel on ebay and buy another tv. Don't break the panel shipping it.

On all input sourses? If so replace main board. If only one source then I would suspect that source.

replace the main board. You can get the replacement main board from www.tvcircuitboards most likley if they dont have it listed I would send a email as they only list boards that they have more than one of single boards are not always listed.

The tact switch is most likely defective which is keeping the volume up engaged. Replace the tact switch should fix the issue. If not the button assembly pcb will need replacement. You can get replacement boards from www.tvcircuitboards.com

The digital volume control section circuit has the fault. You have to check its main digital board. Might need replacement.

Go into your Audio menu on the TV and make sure the TV speaker are set to “ON”.
If the external speakers work when connected to the TV and the TV’s internal speakers don’t work when you remove the external speaker’s plug from the TV, then you will need to replace the main board.
The main board has all the function for the audio for the internal speakers. This was a known issue for some of the LG TV’s. So if you call LG about this issue, LG may fix it under a warranty.
Good luck.

It sounds like you have a defective Main Control board. I would contact a service co. as soon as possible.