You probably have a defective ballast, which is the power supply for the lamp.
If you had the three front LED's flashing, and replacing the bulb didn't fix it, that's most likely what the problem is.
If you turn on the TV and listen carefully near the lamp compartment, do you hear a faint buzzing sound that would last for about 3 seconds, pause for maybe 15 seconds, then buzz again for three seconds? That would be the sound of the ballast trying to fire the lamp.
Another thing you can try to look for is if there is a small blue arc of electricity in the lamp compartment as the buzzing sound is happening.
Or, remove the lamp from the compartment, close the lamp door normally, power up the set, and see if you see this arc of electricity on the spark gap on the ballast near where the wires go to the lamp socket. You may have to take the back off of the set, and there is a safety switch that you'll have to tape into the closed position so that the set will turn on.
The way these lamps work is that the ballast initially supplies about 2000 volts of electricity to the lamp to ionize the gas inside, which conducts electricity, then the ballast will throttle back to about 80 volts to run the lamp.
If none of this pans out, you need to check to see if the ballast has roughly 330 volts DC going to it at the nylon connector with two wires coming from it (not the two red wires that go to the lamp socket). If you have that voltage, then it's probably the ballast. If that voltage isn't there, the problem is on the power supply.
Hope that helps, let me know if you have any other questions, and thanks for using JustAnswer!