Well then it's possible that one or more electrolytic caps have dried out and popped their tops, look inside on the HDMI input board and also in the power supply board, the caps are little metal cans, if they have gone bad then the tops of these cans will have a domed or bulging top.
Do NOT do this with the unit plugged into the AC wall socket, unplug it and wait about 5 min, then take a look.
Also if you do not have the necessary soldering skills I would not try the repairs your self, you may do more damage then good. Take it in to a shop that can.
If you think you can do the job then the caps in question have to be of the same mFd value but can be of a slightly higher DC voltage rating.
Example: A bad cap rated at 1000 mFd 16 VDC can be replaced with one that is 1000 mFd and 24 VDC, but be careful as some of the higher rated DC voltage caps may have larger leads then the old ones, also be careful to get the + lead in the right hole. Get it in backwards and you will have a firecracker on your hands.
And be careful un-soldering and re-soldering them, if you lift a circuit trace your done, the PCB may be beyond repair.