This sounds very much like a hardware fault, to better diagnose the issue.
Please switch it off at the wall, and remove all coax, hdmi and other cables form the TV.
After five minutes, press and hold in the power button on the rear of the TV and turn on the power button. Keep holding the power button in for 5 seconds then release.
If the TV will still not come out of standby, look at the standby light and see if its flashing (if it is count how many times it flashes).
I just wanted to follow up and check if you required any further assistance?
I havent heard from you in a few days, and I just wanted to follow up and check if you required any further assistance?