Hi there happy to help.
First thing to try here is the following.......Unplug the TV for 5 minutes and then retry.
If this does NOT work.......here is the likely cause and fix.......
It's a problem on the power supply(DM module) of the TV.
This generation of Mitsubishi's experience a failure in the power supply board mostly from power outages/surges, etc.....
Problem is that with this old of a TV its not worth a $600 service call.
HOWEVER, you can buy a kit and do this yourself.
Even if you can't solder, you can pull the board and take it to an electronics repair shop where they will do the soldering for around 25 dollars.
So all you have to do is buy this kit, it comes with disassembly instructions as well(which are priceless because they make the job simple.)
Follow the instructions.
Now I have to give a disclaimer that diagnosing over the internet I cannot guarantee this is your only problem. However, like I said, I have personal experience with this, and your 90% or better on a 100 dollar fix here.
Hope this helps,
If this answer helped you please click the ACCEPT button.
When did you make this fix?
The kit I pointed to you above will have all these and pictures of where they are on the board.
excellent good luck.